You mentioned customer service: I understand that others have noticed odd items appearing in "Recently viewed" after contacting CS. It is possible that in the course of diagnosing your issue, customer service might have some sort of supervisory access to your account and that might result in some random listings appearing among your recently viewed. That is just speculation on my part, though. I have no actual evidence one way or the other beyond what I have read on the discussion boards.
I have seen cases where a seller has edited a listing to sell an entirely different product -- that also can cause all sorts of confusion. That usually does not happen very often though.
I agree that if you see multiple items appearing in your "Recently viewed" list that you did not view, that is suspicious, and changing your password is worth doing as a precaution.
