Not the trick step because Harry was definitely not stuck. He kept moving over something after the steps came up.
I vaguely remember something from the first book, that they would climb the stairs to the common room, and then then they had to say a password to get them through the door. That vaguely fits with Harro climbing a staircase, and stopping, and then continuing on. It really looked like he walked or climbed over the barrier though, just skimmed the top, in fact.
Maybe one day I will be watching Harry Potter movies and go “OMG, this is the scene she was talking about”.