I think they personally viewed it as no different than releasing the OG FF7 on PS4, right before announcing FF7R for PS4 a few months later.
Companies do this kind of thing all the time lol.
The thing is, that guy wasn't the only one who leaked it, someone else did as far back as 2020, and everything else that person said turned out to be true.
There was also an at the time ignored 4Chan rumor about Atlus' future output, that as of last month turned out to be entirely accurate, and which iirc does mention a P3 remake as well (not so sure on this, I forget what it said exactly).
Plus, Atlus' own survey has brought it up for the last two years, and usually repeated mentions of something in an Atlus survey ends up being a precursor to it actually happening (Etrian Odyssey PC, Persona 5 Switch, Catherine Switch, 13 Sentinels Switch, Nocturne remaster).
I think it's a reasonable assumption at this point (but of course, should be treated with skepticism until proper confirmation)