Was Desmond Bishop's Hit On Cam Newton Legal?

I've been waiting all week to hear whether LB Desmond Bishop's roughing the passer penalty on QB Cam Newton was going to draw him a fine. It hasn't yet. But Mike McCarthy was asked about it during his press conference he defended the tackle.

I'm not a fan of the way the officials are calling roughing the passer at the moment. It's something the NFL still has to re-consider because it's not working. Quarterbacks are still getting concussed on legal plays, while players like Falcons DE John Abraham are flagged 15 yards on a questionable call where the quarterback was not in any danger of injury. Defenders shouldn't be allowed tee-off but whatever changes they've made to the interpretation of the rule since last year disrupting the game more than helping quarterbacks stay safe. 

Back to the play in question, while McCarthy thinks it's a legal hit, Mike Florio doesn't agree. I know Mike is a Vikings fan who thinks Aaron Rodgers is ignoring cancer patients, but his site is also widely read and NBC is featuring him on TV. Here Florio reads between the lines and came up with this paragraph. From Pro Football Talk:

Bishop and McCarthy seem to think that the flag was thrown because Bishop drove Newton into the ground upon making contact.  While there has been no public comment from the league or Riveron regarding the call, the problem seems to be that Bishop put the top of his helmet into Newton’s stomach.

Why would Bishop and McCarthy think the flag was called because "Bishop drove Newton into the ground?" Maybe it's because that's what the official told Bishop on the field. He threw the flag because "he lifted Newton up." There's no mention of leading with his helmet. 

When officials do explain judgment calls like roughing the passer, they're unspecific and will not discuss hypotheticals. Also, they do seem to be calling it extra tight on hits to Newton and throwing flags on legal hits. The fact that Bishop wasn't fined reinforces the inference that it was a close call, at best.

McCarthy should be willing to stand up for his players, and encourage then to remain aggressive, even when the occasional judgment flag doesn't go there way.