Couple of mums from DD's yr1 class arranged a night out in local pub. Me & couple of mum friends from the class went along as we thought it would be nice to get to know the tohers a bit more. One mum couldn't make it but put a msg on group chat to say we were all welcome to pop in for glass or 2 of wine, but to let her know before 9pm if anyone was coming. It was quite lighthearted though & as we were all in the pub I assumed we were all staying there. 1 or 2 of them mentioned it would have been a good idea if we hadn't arranged to meet at the pub & I agreed. Nothing else about it said. I was chatting to my 2 friends for a bit, then after about 1½ hours of arriving about 7 of them put on their coats & told the remaining 5 of us they were off to this other mum's house. Didn't ask the rest of us if we wanted to come & they had obviously privately messaged the other mum to say they were coming as there was nothing on the group message. I don't know the other mum well enough to invite myself along. So off they went leaving 5 of us! AIBU to think this was rude?