Unfortunately, things like that happen. As time goes on, people change & when they are not in contact with each other over a period of years, they can change in different ways & not be the same 'friend' as they were when they left.
He shouldn't worry too much about it, I know it's easier said then done! But it doesn't sound to me like Joseph was much of a 'friend' anyway, if he didn't even acknowledge Andrew when he got back!
I am sure Andrew had plenty of other friends, including you, that he should now focus his time on! I must say that it is great of you to want to help him out. Maybe he should really re-think who his best friend is