Whilst you're correct you're talking about the Bridge car park and they were talking about the Uni car park on the other side of the A27. Similar reasons though, loads of pedestrians around the Falmer turn off of the A27 getting picked up which made for slower traffic plus just more people than...
I’d hazard a guess of about 20,000. I went to that Palace cup match in 2018 were there were only 12,000 in the stadium and it felt a lot fuller than that.