However, if he really came back into the restaurant 4x, then that is pretty extreme. I've worked in restaurants and seen many angry customer situations. I've never seen any one return 4 times, angry each time. And then his girlfriend comes in to apologise?
That tells me he was out of control. And given that she was strangled a day or two later, I cannot dismiss it as being no big thing.
If the witness was totally making the story up, I think the restaurant employees would leak out a statement or two saying it never happened. JMO