It wasn't a planned firing. This was a spur of the moment owner decision.
Gettlemen was a hardliner (which is why some former players dislike him) business only type of guy. He jettisoned Steve Smith who had lost effectiveness, but wanted money on par with the best receivers. He wasn't nice about it.
He let Josh Norman go to sign a ridiculously bloated contract to a division rival. He wasn't nice about it.
Olsen, the tight end, wants to renegotiate his existing contract and was threatening to hold out (Rosenhaus). Gettlemen seemed disinclined to renegotiate an existing deal.
Thomas, a longtime heart and soul type player (think Fred Jackson), wants a long term contract that doesn't make sense because his play has declined, he has 3 torn ACLs, and is 34. Gettlemen is apparently not a nice guy and wasn't going to give it to him. The owner calls Thomas part of the family and wants it done.
Thus Gettlemen is gone and Thomas will get a new contract.