Nobody was coming round Viviani at that point and I think maybe Bouhanni reacted out of frustration that Jake Stewart was better placed than him in the battle for second.
Edit: this is a better video. Does Stewart lean on Bouhanni a bit at the very start? In which case, it's a bit more understandable.
I don't think it's that bad. Bouhanni gets baulked by his own leadout man, and has to slow and go left to get around his back wheel, as he comes across he bumps Stewart and is knocked slightly off balance, and leans into him. Definitely a disqualification but I've seen much worse.
Nobody was coming round Viviani at that point and I think maybe Bouhanni reacted out of frustration that Jake Stewart was better placed than him in the battle for second.
Edit: this is a better video. Does Stewart lean on Bouhanni a bit at the very start? In which case, it's a bit more understandable.
https://twitter.com/gcntweet/status/1376213337072152584?s=20