DC1 (Yr6) has ASD. He doesn't really have any friends (there's one boy who will chat with him if no one else is around to see, will call for him to play on the Switch if he has no other plans) and is mostly left alone at school. He hasn't been bullied since Yr2. He is never invited to other people's houses, people decline invites to us, has never been invited to a birthday party etc etc. He is not violent, noisy, over-active, obnoxious or anything, he is simply far more childish than his peers and has unusual interests. At break times he plays with the younger children. Most parents are quite stand-offish at parent's events, some resent that DC1 is allowed to use a computer for some work and has a TA for a few lessons a week.
DC2 (Yr5) has many friends and a truly lovely class, and I know I could call pretty much anyone on the class list if I needed help in an emergency. The parents from Yr 6 who do talk to me are those who either also have a sibling in Yr 5 or whose Yr6 child is in a sports team with DC2.
There is a class WhatsApp for Yr5, started by the parents rep and running since Yr3, where random messages about homework and gifts for the teacher pop up. Most recently the return time from the combined Yr5&Yr6 residential. Teacher called first parent on the class list to let them know and parent posted to the WhatsApp chat.
DC1 didn't go on the residential. I find it hard to believe the teacher wrote an email whilst on the coach back and added all 25 other parents individually rather than use the Yr6 mailing list. Especially as he knew DC2 was on the trip. I also don't really believe the parents followed the telephone list and didn't call me because most didn't know DC1 wasn't going. I therefore suspect that there is a class WhatsApp also for Yr6 to which I am not invited.
However, there could be another explanation as to how all the other parents were notified. And the class has the same teacher for two years so there hasn't been a need for a whole group message about an end of year gift yet. Although come to think of there was an issue at the end of Yr4 for the class gift.
YABU - you're overthinking and being paranoid, of course there's no WhatsApp group.
YANBU - probably there is.