Not to nitpick but the description of the mate changed from "good: to “driven and hard”, ie., a hard ass. That changes the narrative. That his replacement was on the dock may lead one to believe the mate was set up. If the mate was “good” the captain could have just as easily had requested replacement AB’s on the dock.
In my world if someone is fired it better be for cause otherwise it can come back to bite you. Perhaps he was encouraged to leave.