It sounds like not much of something to get upset about, but if your boss says the proper dress is a shirt and tie, then that's what an employee is required to wear. If somebody doesn't comply they need to be reminded who they work for, apparently Cam doesn't think rules apply to him. I'll bet he doesn't pull this stunt again.
On NFLN GMFB they're saying Cam said he didn't have a collared shirt, they've made fun of him in that it would've been very easy to find one, and comply with the rule, Cam chose not to. If he does it again I hope he gets benched for the entire game and fined a game check. Some that don't think rules apply to them need to be brought back to reality.