Sure, these games are free to download, but there’s still a cost built into playing them. Or maybe it was an ad for a Water Sort game that does work as advertised, but also makes you watch a video ad in between every single puzzle.
Maybe it was an ad for Hero Wars, like this one depicting a number-based tower game - an ad that bears no similarity to the actual game.
If you’ve played mobile games or even just scrolled through social media, you’ve no doubt seen a misleading ad for a mobile game.