Quest progress (including group members) has been built into the game's tooltip since at least 2013 and can't be disabled, I know this because I had to take into account other group member's quest progress when I was scraping the tooltip for my QuestPlates addon.
I don't know how accurate it is any more, since I haven't grouped with another player on a quest in a long time.
Someone was complaining about it
on the forum as recently as 2 months ago, so presumably they're still in the game.