Disney is pretty widely known to have contracts like this. They basically boil down to “anything creative you do while employed by Disney belongs to Disney, even if you did it outside of working hours.” Because Disney doesn’t want artists, animators, writers, etc to take characters or writing with them when they quit, by claiming that it was created when they were off the clock. That would potentially run the company afoul of IP laws (the same IP laws they lobby congress to make, and wield like a cudgel against smaller creators) if an employee took a character with them when they left.
Basically, if you want to do any personal projects while employed by Disney, you either already started them before you were hired, or you’re going to have to wait until your contract is up.