I mean… technically, sure. They had full access to the computer, they could put whatever software they wanted on it. Realistically, most people selling an old computer don’t give a crap about what you do with it.

If you’re worried, format and reinstall Windows. That’s what I do with secondhand computers, even when I know their history (I work in IT, so occasionally, I’m allowed to take home a machine we’ve decommissioned to play with). It’s always nice to start fresh.