"Shounen magazines never publish gay stuff," and "It's not gay, because it's in a shounen magazine," seems a bit like circular reasoning...
Actually, overall, expanding a bit on what I said before, this seems like a very interesting case with regards to tagging. (Assuming it continues on its current trajectory as of Ch. 2)
I mean this could still pull an (unconvincing?) "no homo", or, I suppose, an unexpected-gender reveal. But basically the entire joke is that the inspector has a mad crush on the bloke. If homophobic social constructs didn't prevent everyone in the room for calling him out on it—for instance if the thief were some femme-fetale instead of "Kaitou Jack"—it wouldn't be funny.
(And the reason it's socially acceptable in a shounen mag despite being gay is only, frankly, that the gay character can be seen as the butt of the joke. For the homophobic readers, the entire gist of the series is just, "haha, gaaaaaay")
Even assuming that the chapters continue like this, though, I can see the argument that it's not shounen-ai because it's implicitly understood that the inspector's stalkerish love is there strictly for comedic (not romantic) purposes (and that it is implicitly understood that it will always remain unrequited to keep things in "good taste"). But that argument at present also relies really heavily on social constructs surrounding where the story was published, not anything in the work itself. To the extent that it matters, then, how much do tags care bout authorial/editorial intent instead of actual content?
So, for instance, if you showed me the same story in a shounen magazine except with one of the two as a girl, I'd assume their romantic prospects were decent, and might be inclined to call it a romcom...