I took a look at the video and yes, that heavy looks fishy. It wouldn't be the first time I see something weird happening in this game though. It'll take more than that to convince me, as I'm sure it'll take more than my word to convince anyone. Videos uploaded by other players that show it happening in other situations would be a good start.

The best way to clear any doubt would be for him to stream while he's PvPing. Obviously, as soon as his win rate would drop, which is already happening, people would just scoff at it and say he just stopped using whatever he was. People have no idea how much PvP experience he actually has. I actually think that him streaming would actually be very beneficial to the community as a whole, because when I started PvPing, he gave me a lot of solid tips that I haven't seen in most of the "help me play better with my class" threads over different forums and reddit.