It was an unsportsmanlike conduct for a coach on the field - that's what was announced as I recall. I thought the deal with Cobb was a good no call - he signaled the fair catch very late, the ATL ST player made every effort to avoid him, and he caught the ball cleanly. The conduct penalty was kinda silly, but probably technically correct.
If that really was on Slocum for being on the field they can call that every week on every team. Totally bogus call.
But Rodgers leads the league in frumpy expressions and negative body language on the sideline, which makes him, like Josh Allen, a unique double threat.