Stars 20+2, flop top and bottom 2pr, painful turn

[mason55]

Villain had just been moved to the table a couple hands ago so I had no reads (always seems to be the problem). I hadn't been getting out of line and neither had anyone else at the table. The table had been playing passively but I don't know about villain.

Blinds 15/30
Villain is on the button with $2400, I am in the small blind with $2200.
3 limpers to me including villain, I complete with A5s, big blind checks.

Flop (Pot $150) comes AT5 rainbow, none of my suit.
I bet $100, folded to villain who calls.

Turn (Pot $350) is a K, completing the rainbow. I bet $300, villain makes it $1000.

I think this fold is much easier than it appears at first glance but I'm curious what others think.