I think there's 2 reasons why he goes all in:

1.) He has the flush draw
2.) He has a set (or maybe a s8) and just called the flop to build the pot. He then saw the potential flush draw and got scared, so he pushed.

I call. If he has you beat with the set, then sht happens. If he's on the flush draw or a bottom 2 pair, then you played it right.