if the vidic tackle you mean was the one where people were screaming "he's the last man" then it was ayellow as cole didn't have the ball nor seemed likely to be first to it had he not been fouled.
Frankly, I don't understand the rule. Is it a red for denying a goalscoring opportunity? Does anyone know what constitutes a goalscoring opportunity? I'm pretty sure reds are dished out if you get fouled when being one on one, regardless of the control of the football. Is it just poor application? QUESTIONS?!