Ugh... river donk

[Aaron W.]

This happened a couple weeks ago and I just wanted a sanity check:

Bellagio 15/30

I open AJo as either the CO or button and get called by one or both of the blinds. The flop is AQ9 monotone giving me the J-high one card flush draw with my top pair. Checked to me, I bet and get called by one player. The turn is a suited T completing my second nut flush. Checked to me, I bet and get called. The river is an offsuit low card and villain donks. Villain seems like an okay TAG so far. Nothing special about his aggression that I've seen, not super-loose, and nothing incredibly stupid.

Is this an auto-call despite all of the high flush cards being out?