You don't throw it, not the same as holding on every play..
Illegal man downfield is a point of emphasis by the NCAA this season. They instructed officials to call it. They told coaches to make sure that their players knew that if they did it it was going to get called. And for the most part officials are calling it. It was called twice on the same team in one of the games I was watching last weekend.
But I agree, it isn't the same as holding, which could (and in my opinion should) be called a lot more than it is, but has a lot of officials judgement to it. Illegal man down field is cut and dried. The lineman either has gone too far or he has not. In that case Johnson went too far. It was a penalty. Go back and watch it.