Totally agree with everyone else that ... things are being left out here. I mean, look at this:

I feel I should've been informed of the child's orientation being such an important aspect of his ... or rather, their identity

And there it is. The LW's excuse isn't even "I didn't know that they were non-binary" - which would raise my eyebrows anyway, given that this was a friend's child's party that they were invited to. Their excuse is "I didn't think their gender identity was important."