Victory would have seen Wakefield open up a three-point cushion over their opponents in sixth.
They were on course to do that after opening up a 10-point advantage, but three tries in 10 minutes changed the outcome as Hull won at home for the first time in almost 12 months.
It led to Powell questioning how the flow of the game was altered after what he believed were comments made to the match official during the break.
“There was an influence on the referee,” he said. “I just thought the game completely flipped.
“I’ve seen an influence on the referee in the tunnel first half. I’ve done that in the past. It just shouldn’t work and I think it worked.
“The referee completely flipped his decision-making. We got no penalties in the second half, I’m not sure they got any in the first half. It probably should have been a little bit more even either way.
“Did that have an influence on the game? I think it had an influence. Is it the main one? I just don’t think we handled the second half well.”