Harry and Ron are nowhere to be seen, Cho is crying at the Ravenclaw table but no one is calming her down, they all ignore her and give her nasty glances. It is clear that she is the reason that the group got caught, but I expect that something must have happened for her to spill the secret. Was that piece of parchment a list with all the names or something like a contract? It is very stupid to write down anything that can incriminate you, unless it is bewitched with very dark magic.