Forum:Exiled Forces Question

I ran into a situation a few days ago when my oppenent played Exiled Force while I had a face down trap hole on the field.

After he summoned exiled force he said something about calling priority while I was flipping up my trap card and said that the trap hole wouldnt matter because he was supposdly tributing exiled force before trap holes effect would hit it

My question is is this even a legal move? I figured that for exiled force to be properly tributed its summon would have to finish complelty and thus my trap hole should have stoped the move dead in its tracks

NOTE there were no other cards on his back field or my back field and the card he destroyed was white horned dragon