The guy didn’t either remember at first, being a vegetarian was a small detail she mentioned on the phone once.
He only realized when he was trying to figure out what would have made her act like that in front of him and his family (especially if she honestly thought she was going to marry him). In general there is nothing wrong with being seen by your date and his family while eating with friends.
If anyone out there knows her would you mind letting us know her side of the story?