tuff spot, sorry...
Is he holding a 7... I don'T know. Did he hit a str8 on the turn (with 9-10), I don't know.
Did he hit a J, and wants to find out where you at ?

From the betting battern here, I'd fold. But like dave said, it's nl5, so you can be facing any 2 cards. The reason I'd fold might sound stupid here but it's because btn is willing to go to war here (all the way) and has a mid size stack (ready to lose it all), + he did not cared the fact you raised UTG.