I'm impressed his former boss sent him a note to state that he felt really bad about the way things happened. It would be nice if he'd done more initially but it still takes a lot of character to write that note and apologize vs just blow it off or chalk it up to the past.
I disagree. There was nothing to lose by sending this and everything to gain. There was no character required to write an apology when you're no longer near the situation.
I suspect he's just trying to rebuild burned bridges for better networking in SF (he just moved there).
