Some of the prophecies in the Bible are self-fulfilling. By that I mean that if someone is aware of the prophecy, then they can fulfill it simply through conscious effort. For example, it is prophesized that the Messiah will enter Jerusalem on a donkey. That prophecy is found in Zechariah 9:9. It is fulfilled in Luke 35-37 and Matthew 21:6-11.
If Jesus knew of that prophecy (which he probably did) then the odds of him fulfilling it are 100% (at least as long as there were any donkeys around). So even if this event really took place it lacks any significance.
This is the case with some of the other Biblical prophecies.