This is simply untrue. The vast majority of piano technicians today do not have vision impairment. It is true that piano tuning was historically one of the better career options if you were blind, but then that has changed. Thanks to modern technology a lot more options have opened up. See for ex. this article about one of the most famous schools for the blind closing: spokesman.com/stories/2017/mar/10/…

It's entirely possible to learn, but you're really trivializing lever technique. It's just not that easy to get the tuning pin and string to go where you want it to. You gotta develop muscle memory for it -- getting through all 200+ strings the first several times is a pretty exhausting experience.