Frequently it will say my friend is playing something that they straight up aren't. The same has also happened where it said for them that I was playing something I wasn't. Sometimes refreshing the page fixes it, but sometimes the bug persists even through that.
This bug has been here for months, probably ever since I started playing a year ago.
I've suspected that they may sometimes "inherit" what a different friend in the list is playing. But that's just my theory.
Attached image of someone I know IRL who is literally asleep right now and definitely not playing any map whatsoever.