To me, your question looks quite acceptable for MO.
"Research-level" is a slightly awkward shorthand and shouldn't be taken too literally. I like to picture the typical intended user of MO as one who is a "serious student of mathematics", where mathematics professors are counted as being among "students of mathematics", and "serious" might mean (roughly) "past the qualifying exam stage of graduate study". So if such a user is studying some bit of mathematics, gets stuck on something and doesn't see a solution after some thought, some googling, etc., but feels it is very likely that some other serious student has worked through the details and can handily provide an answer, then chances are the user has a question tailor-made for MO. The linked question sounds like just such a situation.
Of course, there are situations where not everyone can agree on the criteria for being "MO-worthy". If in doubt, it's always good to ask here.