Can these statements really be arguments?

Yes, I wouldn't call them arguments. The answer key marks them both as "Argument (Explanation)." I'd say this book is wrong; explanation is different from argument.

An argument must have premises that support a conclusion.

Samsung stole some of Apple's patents for their smartphones, so Apple stole some of Samsung's patents back in retaliation

This cannot be divided into premises and a conclusion. It is better understood as three unsupported premises:

A. Samsung stole some of Apple's patents for their smartphones.

B. Apple stole some of Samsung's patents.

C. The cause of B was retaliation for A.

It is not the case that A is a premise from which we would conclude B; that would be a non sequitur. Apple could have done any number of things other than stealing Samsung's patents. And we are not trying to infer what Apple did; it is simply stated as historical fact.

The reason I forgot to lock the door is that I was distracted by the clown riding a unicycle down our street while singing Lynyrd Skynyrd's "Simple Man"

Similar situation. Three unsupported premises, none of which allows the inference of any other:

A. I forgot to lock the door.

B. I was distracted by the clown riding a unicycle down our street while singing Lynyrd Skynyrd's "Simple Man."

C. The cause of A was B.

Conifold properly identifies an important distinction between happenings and inferences. Happenings are when one event precedes and seems to cause another event. An argument is when inference from premises preserves the truth from premises to conclusion. We can represent them both by arrows:

Happening: Event A -> Event B
Argument: Premises -> Conclusion

Let's look at the difference.

"The reason I forgot to lock the door is that I was distracted by the clown riding a unicycle down our street while singing Lynyrd Skynyrd's "Simple Man"."

Event A: Clown riding and singing ->
Event B: Distracted me ->
Event C: Forgot to lock the door.

14:"Samsung stole some of Apple's patents for their smartphones, so Apple stole some of Samsung's patents back in retaliation.

Event A: Samsung stole patents ->
Event B: Apple retaliated

In both cases, we have a sequences of causes, not a sequences of inferences. To be an argument, it's not just a true statement followed by a true statement, but rather it is true statements that logically entail true statements. The former shows a temporal and causal relationship, and the latter shows an inference.

Just to ensure the difference is clear, here's an example of an argument:

P1. Socrates is in the kitchen.
P2. The kitchen is in the house.
C. Therefore, Socrates is in the house.

Notice how these are not events, that is not claims about cause or time, but rather capture how when the first two things are true, the third thing must also be true. And that is what the author is trying to get across.

The reason I forgot to lock the door is that I was distracted by the clown riding a unicycle down our street while singing Lynyrd Skynyrd's "Simple Man".

This is an explanation, not an argument.

Samsung stole some of Apple's patents for their smartphones, so Apple stole some of Samsung's patents back in retaliation.

This is an explanation, not an argument.

In an argument, you start from what you think is a fact (the premise), for example "He was at the party", and you propose what you think is a conclusion which follows from the premise, for example "He must have seen what happened". Thus:

He was at the party; so, he must have seen what happened.

The audience must be uncertain of the truth of the conclusion. You don't try to convince people of something they already believe.

In an explanation, you also start from some fact, but this time one to be explained, for example "He arrived late", and you propose what you think is a good reason from which the fact to be explained follows, for example, "the traffic was terrible". Thus:

He arrived late because the traffic was terrible.

In an explanation, the reason offered to explain something may be a known fact or a conjecture. If a conjecture, however, it should be verifiable, at least in principle, otherwise the explanation has not value to anyone. "God did it" may explain everything, but it is unverifiable so it has no value.

Explanation:

Apple stole some of Samsung's patents (fact) because Samsung stole some of Apple's patents (again fact).

Argument:

Samsung stole some of Apple's patents (fact); so, Apple will probably stole some of Samsung's patents (not yet a fact).

Explanation:

I forgot to lock the door (fact) because I was distracted, and I was distracted because a clown was riding a unicycle down our street while singing Lynyrd Skynyrd's "Simple Man" (verifiable).

Argument: A clown was riding a unicycle down John's street (fact); so, he must have been distracted (uncertain).