Not sure either linesman had a good view of it either to be fair, it was in the other half to the linesman on that side, and the far side of the pitch from the linesman in that half. The original broadcast view of it live it wasn't obvious that Mitomas right leg had been caught as all, looked...
I think Wilder knows full well that its a shocking "tackle", and his comments are to try and reduce the chances of his player getting an extended ban for it. I think it warrants being more than a 3 match ban.