His river bet certainly doesn't suggest 'flush'. It suggests pair/2pr/failed draw afraid to waste too much money if they're up against a flush.

A 16/4 probably won't call a raise without the flush, so the passive line is probably how I'd play it. I might raise the river if he was more stationey and think he'd look me up with 2pr or less, but I think the flush out there's killed your action against any semi-thinking player...