Also true. But we must consider the fact that when the show was airing, though I’m sure non-binary people certainly must have existed at the time, non-binary was not something that was part of the mainstream consciousness. So would not have been acceptable in a kids show. And though I’m not sure it would even be acceptable in today’s day and age by most mainstream standards, it’s more acceptable now than it was 30 years ago.
On top of that it’s very likely that most real people at that time who would likely identify as non-binary would not have identified themselves as such and would have chosen a he/she pronoun of some sort to identify themselves in order to conform to the social standard of that time.
Still, we should celebrate the characters who are designed to be nonbinary, to represent that community, not try to decide for that character 30 years later.