No, riding a donkey in Jerusalem does not make just anyone a messiah; Matthew 21:4–7 presents a unique fulfillment of Zechariah 9:9.
Zechariah 9:9 — Rejoice greatly, O daughter of Zion; shout, O daughter of Jerusalem: behold, thy King cometh unto thee: he is just, and having salvation; lowly, and riding upon an ass, and upon a colt the foal of an ass. (MT)
Zechariah 9:9 Rejoice greatly, O daughter of Sion; proclaim aloud, O daughter of Jerusalem; behold, the King is coming to thee, just, and a Saviour; he is meek and riding on an ass, and a young foal. (LXX)
Matthew 21:5, 7 — Tell ye the daughter of Sion, Behold, thy King cometh unto thee, meek, and sitting upon an ass, and a colt the foal of an ass. [The disciples] led the ass and the colt, and place garments on them, and He is seated upon them.
Mark 11:7 — And they are bringing the colt to Jesus, and they are casting their own garments on it, and He is seated on it (colt).
Luke 19:30, 35 — saying, "Go away into the village facing you, in which, entering, you will be finding a colt bound, on which no man ever is seated, and loosing it, be leading it to Me. And they led it to Jesus, and tossing their garments on the colt, they mount Jesus.
John 12:14-15 — Now Jesus, finding a little ass, is seated on it, according as it is written, Do not fear, daughter of Zion! Lo! your King is coming, sitting on an ass's colt.
Zechariah mentions both an ass (likely an adult donkey) and a colt (probably a young donkey), emphasizing humility and peace rather than the logistics of riding both at once. In Matthew 21:7, Jesus most likely rode only the colt (cf. Mark 11:7; Luke 19:35; John 12:15), while the ass accompanied him; both are mentioned to fulfill Zechariah’s prophecy, not neccessarily to suggest he literally rode both. In ancient Israel and surrounding cultures, it was common to travel with a led or pack animal alongside the ridden animal. The Greek word translated “them” (autou) is ambiguous and can refer to one or both animals. However, it would've been awkward and unlikely to ride both because young donkeys (colt) and adult donkeys (ass) are not of the same height nor stride.
In other words, the “them” in Matthew 21:7 does not necessarily mean Jesus rode both animals; it likely reflects Matthew’s chosen wording in contrast to the other Gospel writers. For example, in Matthew 26:8–9 and Mark 14:4–5, the disciples’ indignation over the woman anointing Jesus is described generally, while John 12:4–6 specifies Judas as the one who objected. In a similar way, Matthew’s use of “them” may reflect a general expression rather than a literal statement that Jesus rode both the ass and the colt. General wording ("them") in one account doesn’t preclude specifics that other writers provide ("colt").
The Gospels present a profoundly beautiful image of Jesus, an approximately 33-year-old man (cf. Luke 3:23; John 2:13; 6:4; 11:55), humbly riding a young donkey (colt) as the King (cf. John 12:13, 13:14-15; 19:19). True power expressed through humility (Hebrews 2:9–10; Luke 19:36-44)