[SharkSandwich]

I'm calling the river for sure. It looks like a bit like a blocking bet, because he doesn't want to get bluffed out with a larger bet he can't call.
And the way he backed off after the Turn hits the 4-flush this looks more like a set than anything else.

Yeah I call this at this size for sure against an unknown. He only needs to not have the flush 1 in *5.5*, and there's a lot of flushes that wouldn't bother betting there.

If the bet was bigger I'd have more of a decision.