He could have flatted with AK, KQ, 88 is also a possibility. Unless he's a trapper, flatting with AA or KK preflop, then seeing the two hearts decides he can't slowplay anymore and risk everyone checking behind. With only you having to close the action, he might feel comfortable enough to play the pot with the guarantee of it being 3-way and only a small risk of being outflopped.
He could have AhQh, willing to gamble with what he thinks is decent equity, given you saw him stack off light on the other table. But would he have donked the flop though, hoping seitafang had QQ/JJ/1010 and wanting to take it down right there? Most players would usually check to the preflop raiser.
You're losing only to KK if he slowplayed them preflop and 88, he can't have QQ, and you're beating AK, KQ, and AA (again, if he slowplays them preflop), and AhQh if he would just donk out instead check-calling.