It's the timing of an opponent who is playing lightening fast and then suddenly stops and abandons the moment they blunder a piece. It doesn't happen often but when it does it's clear they have abandoned because they're in a losing position. Similar behaviour to how opponents abort a game when they start as black because they only like playing as white.
I don't have other windows open when I'm playing a live game in-case it appears suspicious to fair play detection or the site thinks I've abandoned.
Just as in life, you have NO idea what's going on at the other end. A phone call, a child crying, an angry parent or spouse. So relax, play a puzzle in another window (if you're on a computer), or read a news feed if you're on you're phone. There are a lot of worse things that could happen to you, than have to wait a couple of minutes.