My theory is that this could be hinting towards Ibarada's graduation or the series ending. Ibarada graduation theory is pretty straightforward. Series ending theory goes, manga lifespan are usually 10 years and this has been going since March 2016. I think we will get our answer by March 2025 at the 9 year mark on what this was hinting towards. But this is purely a guess.
as a certified Math Nerd Tee Em I really like this manga but I have a big pet peeve about it. it's so anti-null-hypothesis. If you can't prove something conclusively, PUBLISH IT ANYWAY!!! THATS STILL GOOD INFORMATION!!!