Yeah this does not feel like an ending at all, 10 chapter sequel is a bit too short to qualify as official works (from a reader's point of view). I seriously doubt it was the mangaka's decision to end it here, as it's not that great of a spot to leave everything off and I can't picture this being "oh, I'm kind of bored of making this so I'd like to end it here". I really liked the prequel, so I was looking forward to starting this, but where it left off at feels like a letdown. I guess at least its ending wasn't as ridiculously illogical as Dagashi Kashi's.