)
Unless contradicted by the show, the show runners' statements are just as canon as is what is in the show directly.
The show does not conclusively prove what gender Li'l Cheese is, so Word of God on him being a colt is canon.
Exceptions to a rule _*literally_* prove that a rule isn't 100%. That's how logic works.
Finally, you might want to brush up on what faith means, because I am operating on exactly the opposite of blind faith here.