It depends how smart the tang is.
IMO if the tang is new to the tank it might be using that little space as a refuge.
If it just got stuck, then he might need a helping hand.. but i doubt it got stuck..(accidently)
Does he look stressed out? is he breathing rapidly?
I think if it was stressed out, it woudn't be eating..However i dont see how tangs would enjoy being cooped up...just a though..