I think you played it o'k if you folded river. You can beat a complete bluff and how often do people take these lines with air ?

I think I'd fold river, especially when the flush comes in, but you probably need to call some Ax here to avoid overfolding. Good ones that come to mind are hands like AxKd AxQd not only because it has a good kicker but also because it blocks flushes much more than your 4d does.

Villain's line is good. This is the logic I'd apply (why he's doing it, who knows). When the pfr cbets it's unlikely they have many Jx since many players tend to check those back these days. Therefore the Jx turn will pretty heavily favor the caller who has every Jx in his calling range so it's a good spot to lead with both strong hands and bluffs.