The "magic skateboard" was a Trickster Mentor.
It only gave Tyrone incredible boarding skills when he first found it to set him up to honestly believe it was still doing it during the contest. After the first two rounds, it decided to abandon him before the third, therefore setting him up to knowingly win it on his own after unknowingly doing so on the last two.
Uniqua is an alien
The Backyardigans actually are reality makers
Allow me to elaborate, the 5 members of the crew actually have a limited reality creation skills, while using their imaginations, they are able to actually create a pocket dimension to play in, explaining the fact that everyone percieves the world in the same way.