First of all you should have asked what he wanted to do with the laptop, the moment he replied playing games that are not on Steam you should have let him use Windows. Secondly, a laptop with 256GB of disk is likely going to have very low amounts of RAM and an onboard GPU, performance is going to be shit on Windows as well, you should have let him use that before, I think it’s highly likely that Windows itself would run like shit on it, so after a year or two putting Linux on that laptop would have blown his socks off. But the problem is that he didn’t get to experience any of that before you touched the computer, now he will claim it’s your fault that games don’t run or Windows is slow. I’ve been there, a friend had issues with the laptop, I said I didn’t understand Windows and would only help if I could put Linux, at first everything worked great, but then the friend needed special software that wasn’t available so I had to reinstall Windows for them (and btw, you OBVIOUSLY should reinstall Windows for your friend), and then everything on that laptop was my fault, even the problems the person was having before were somewhat my fault because I had put Linux there.