At least in Germany that's the case.
Every contract is legally binding in Germany, even verbal contracts or in this case price tags (to some degree). Obviously other laws may invalidate them and verbally is hard to prove. For example if you advertise onetime off prices for a week to lure people in the store you have to have a reasonable amount of these items to be available through the week, otherwise people are eligible to get the offer or compensation.
Adding your own sticker would probably be fraud and easy to prove for the store (not matching sticker, no plans to reduce prices, ...).
As someone who had a mildly unpleasant interaction with kernel folks, I can totally understand the issue.
This is one of the very few open source projects I had the feeling they don't appreciate new contributers. There is no on boarding material available and picking the wrong subproject mailing list results in being ignored. You have to spend days without any possibility of help and if your are lucky you get mentioned as a reporter. For the next issue you start from square one as there was no guidance, so you could only learn the bare minimum.
So yeah, his patch may be underwhelming. But the help and credit he got for days or weeks of unpaid work was basically nothing. You may be okay with spending days and only getting credits for the bug report, but I suspect many aren't and will not contribute again after such an experience. And post like this try to point out the issue they have and why many people won't contribute to the kernel ever again.