I am in shock. How do you inspire learning when a child is faced with that kind of opinion. It sounds like the teacher has a personality conflict going on with your child.
I know this is personal, but how many birthdays have you being invited to lately?". Continuing further - "How many play dates have you been on ?"
That is as inappropriate as a student telling a teacher "do you know how many students pretend to really like you?" Why such a focus on popularity instead of 'learning', acceptance, and a safe environment.
I would bring it up so she doesn't do it to another student again. Hopefully your son has already forgotten the conversation and dismissed everything she said.