He is using some sort of click-bot, he automatically starts hitting you as you get close to him as demonstrated in the video. As you can see, he gets way more hits at me than I do at him even though I'm spamming both my touchpad and mouse to aim fully kill him. It's happened to TheKrafter1923 too beforehand, and many other people too that just haven't complained about it yet.
Here is a video for the sake of proof: