lol, both looked back. So even if they didn't hear it, which i do not believe for a millisecond, they very well knew. They didn't know how bad it was? Well, there were 4 of their team in front, and one is missing, that means the crash happened A/ to/with their missing teammate B/in the very front of the peloton. So they knew there was a crash, and with a crash in a sprint you know it can potentially be bad. Furthermore, their teammate missing should have been enough not to start cheering like idiots. Also, what is there to cheer about? Yay, we won a race because everybody else crashed, but let's pretend we didn't hear, see or understand what was happening when suddenly nobody else was following or sprinting? Good show boys. A proud moment to cherish.
I can understand that they were a bit confused and everything happened so fast, and riders, especially those that don't win too often, have their DNA modified to cheer when crossing the line. Just don't expect me to buy that hogwash that they had no idea what happened.