I saw more of an awkward guy doing a weird gesture, either because he was trying to be edgy, or he meant it as something else. He might even have done it as an ill advised joke because people were already calling him one.

It's silly to call him a nazi because he doesn't fit the profile well at all. It only works if you redefine nazi to be whatever you don't agree with at the moment. This might even be harmful, as it's an obvious strawman that provides cover for his real faults.

He denies being a nazi. We can take his word on that. One thing about nazis is they are weren't shy about their beliefs.