Wasn't exactly what I saw.
As you said, guy ended up on track. He looked a bit surprised when he realised where he was and it looked from where I was (albeit quite a distance away) as if a steward told him to get back because the guy just started walking back. Then a steward, don't know if it was the same one or a different one, decided the guy should be ejected and started moving quickly towards the guy. The guy tried to get back amongst the other fans but got caught by the steward before he made it to safety. Then the tug-of-war started and Police Scotland arrived on the scene to help the steward out and throw the guy about a bit.