The coach was sent to the stands by match official Gianluca Rocchi as his Porto side, leading 1-0 from the first leg, were blown away by a Sevilla outfit that raced into a 3-0 lead inside half an hour.
Ivan Rakitic's early penalty, plus further strikes from Vitolo and Carlos Bacca put Unai Emery's charges in complete control at the interval.
Despite the hosts having Coke sent off early in the second half, Porto fell further behind to Kevin Gameiro's tap-in and Ricardo Quaresma's late thunderbolt was no consolation for a fuming Castro.
"I think the referee acted in an arrogant and boastful way to me and to the players of Porto," he said.
"The penalty that lead to the (first) goal did not exist. The penalty turns out to be vital for the outcome of the game.
"We tried to play, but Sevilla pressed too high. The second goal was difficult to digest and the third rocked us completely emotionally.
"The second half was clearly ours, but this was a night where nothing went well."
