A recent update in CS2 added a new feature when looking for a match. Players now see how many people are in the same queue so that they can better understand a possible long waiting time. Dataminer Thour asked the devs about the exact meaning of the displayed numbers.
The game doesn't display every player who looks for a game. The numbers reveal only those with matching parameters. Users looking for a game on Train in Competitive won't see people who search for other maps. Nor will they see players from other regions even if they look for the same game.
Valve doesn't explain what are the "other details." Thour suggests this might be a player's Trust Factor. Even though CS2 devs are more secretive about this system in CS2, Trust Factor works and restricts suspicious players (multiple accounts, bots, possible cheaters), placing them in separate queues, according to the official support page.