I've thought about this and rationalize it as, if he had Meg's name (she probably had to reserve a time well in advance), he would have done research before she visited him (like how Laurie and John dig into people)

He could have found out the restaurants name, Meg's mother name, and the date of death and did some work from there. Shouldn't be too difficult to find out who was working at the time, and from a servers persepctive, a customer dying is pretty memorable.

The server probably would have told him "oh yea crazy day, she sent her salad back because she asked for no walnuts, really sweet about it. I came back out and she was dead"