This is a fairly common setting for Reiwa LN romcom series. I'd run off a fairly long list but most of their manga adaptations haven't quite reached the dating stage yet. Hookup Hiccups is one exception that comes quickly to mind; KimiZero would be another.
TBF, her moods have always been a bit on the unpredictable/inexplicable axis. This behavior isn't as much of an outlier as it might be in other titles.
I forget if it was the first chapter or the second, but we do get a memory montage of her eyes being constantly drawn to him throughout their first year.