Ladies whenever your boyfriend or husbands mothers hates on their own son to you... Remember she is not doing it for your benefit. She likely doesn't like you and wants to convince you to break off the relationship because of that. If she loves you for her son she will always say stuff that is meant to help your relationship out.
Alternatively, she could one of those Son husband type women who is just jealous of you. Regardless the same principle applies. They just don't want you around. Nothing to do with the son, because if the mom really didn't fukk with him like that she wouldn't even bother having a relationship with him or meeting his girlfriend to offer advice.
Regardless you should walk out of a convo like this feeling disrespected, not thinking you learned some valuable info about your man.