(As a preface, I have no skin in the game with this particular question. I was just browsing and thought it looked interesting, but can't figure out why it's off topic.)
The question Why do I turn into super Mario instead of fire Mario when I touch a fire flower AS SMALL Mario in Super Mario Bros 1? was posted two days ago, hit the hot questions list, and was eventually closed as off topic. There's no comments under the question indicating why it's off topic (possibly they were cleaned up by a moderator.)
It's basically a question about a game mechanic, which is on-topic according to the topic list in the FAQ linked from the close banner. Basically it's in the form "when I did X, I expected Y to happen, but instead Z happened. why?" There are two answers -- one incorrect, and the other a bunch of source code. Neither is particularly good, which shouldn't be relevant to the on-topic-ness of the question. I'm ignoring all the votes because as a former HNQ question those are all suspect anyway.
This seems like a perfectly legitimate question to me. It's perfectly answerable without decompiling to source -- obviously reading the source code will confirm the answer. It could even be answered without referencing the source at all, and instead by just stating the facts ("You only transition to fire state if you start off as Super Mario; if you're Small, you transition back to Super; if you're in any other state, nothing happens." etc.)
Why is this off-topic?