On mobile (tested on iOS, iPhone and iPad), a game’s playercount will show how many players are online. However - on the game’s details page, it displays the platform specific playercount.
See: 302 players in World Zero
After tapping on the game:
I’m assuming this is a bug, since there is no benefit to telling the user there is less people to play with? Mobile users are able to chat & play with all PC users. So the only person the platform playercount should matter to is the developers!