Seems they do not bother to read, before clicking.
It literally says Name your own price, next to the button does it not?
And then
This game is free but the developer accepts your support by letting you pay what you think is fair for the game.
No thanks, just take me to the downloads
I read a lot of comments on games, and I do not remember encountered people complaining there, that they thought a pay what you want game was paid. 10% sounds substantial, so I would expect to see this issue popping up here and there.