Nothing in the protocol changed. There is absolutely 0 change to Bitcoin protocol. They did not implement any changes to the protocol. This is not a change! Since they did 0 change to the protocol, they did 0 contentious change to protocol. Since they did not do a contentious change they have stuck to their work so there is no hypocrisy.
A protocol includes both the syntax and the semantics of messages. The semantics includes the dynamic behavior of the nodes and the meaning of the messages. In particular, prior to this change certain messages would be rejected by nodes and not forwarded. Subsequent to this change these messages will be forwarded. Ultimately this effects what users will see. RBF changes how nodes work and the functionality of the bitcoin system.
It does this because it changes the protocol.The confusion here comes from coders looking at the mechanisms inside one node and not seeing a larger picture, which includes the combination of many nodes with applications software and ultimately the human users of Bitcoin. A further source of confusion comes from the lack of a Bitcoin protocol specification and the lack of a process for evolving this specification.