^But it wasn't something they had time to go into in the story. It would've been a needless distraction. So they just reduced it to a throwaway "seems familiar" as a nod to the old-school fans. There's no reason to see it as some kind of important plot point about the Doctor suffering memory loss. It's just a matter of storytelling logistics.
Sure, but that doesn't mean it can't also be used for a different purpose, i.e. foreshadowing.