+1
As is the case with nearly all these questions, there is not objective answer. There is no official register of what qualifies as surreal, funny, interesting, or anything else. There are just people's opinions, really. If you're just asking people for their opinions, fair enough, but the phrasing often implies that you think of this as an official designation or something.
You're not going to be able to find hard rules for any of this stuff. If you ask the question and expect definitive rules, you're going to come back at every helpful person with edge cases or exceptions that drive them nuts, because they understand they're giving you general principles and not hard rules. Which is all that can be given in response to something like this.
That said: I'm not sure Oldboy would qualify for me (or most people), because I don't think being unrealistic for our world is enough to qualify as surreal (even if that would seem to satisfy a dictionary definition). Superhero films are similarly implausible but nobody would call them surreal, because they establish rules and are effectively inserting unrealistic events into an otherwise predictable and realistic world. Surreality usually means question even the internal sense of logic.