This one user I've never interacted with is consistently showing up on my home page and it's freaking me out

I'm not gonna show or say who it is, but they and like two other users are the only ones who keep appearing at the top of my home page at any given time. I know the other two who keep showing up, but I have no idea who this other user is. No memory of ever interacting with them or even seeing them around! And there are people I interact with all the time who don't show up on that thing. What the hell?! 😱