Just shared some words with Arthas now and after taking a look at the evidence provided by you, I can say that, he didn't do that on purpose. If we watch it carefully, you will come to know that there were people around whom he was trying to hit during the last few seconds of the video but probably you got popped mistakenly.
We can find Arthas at the same position throughout the video being aware of the fact you are in the same room. He did not hit you before maybe because he was aware that it's prohibited and at the same time not being aware of the bullets can pass through glass. I spoke with him just now and it appears to be what he said is truth. Further, evidence recorded by me:
https://youtu.be/LSrWLwSGmS0There is a confusion among a majority of players that whether hitting through glass is allowed or not since wall glitch is automatically disabled by the server. I'll discuss it and maybe rule will be posted regarding that but for now, I'll go with a warning as it was un-intentional. I'll keep this open for a little while if you have anything to say.
VC-MP: 
