I don't think it means he has visual issues. He just thinks his fingers look neat when he flicks them!
I have a lot of visual stims, too. If I walk by something that has a moving light pattern, I could stare at that all day long. Sometimes, things are just fascinating to watch, so we get mesmerized by them.
For example, I used to squint my eyes and look at streetlights, and it would make them look tall. If I tilted my head, it looked like they were dancing. My mom thought there was something wrong, but I just liked looking at how the lights went when I squinted my eyes like that.
Don't worry, it's most likely something that's completely normal for an autistic person
if you think it might be serious, you could check with a doctor to make sure, if you're able to. I wouldn't worry, though.