The answer makes a difference in this situation. I can't link to them. The contract probably doesn't cover anything to do with you - nor should it as the contract is between the company and their customers. The devil is in the details which both of our resident attorneys will pipe in to confirm. Put the shoe on the other foot.
Ethics are subjective.
I think this is more of a legal issue. I don't see what the big deal is unless there is bad blood here that isn't being detailed. If they are mad at your departure they may be hell bent on giving you a hard time. No because our contract states I will be showing our works in our portfolio and that our independent contractors can do the same. But then again, I am the owner of the company and set the rules.