how is this even possible?

So many people are saying that shooting a person behind a gun shouldn't do damage. THEN EXPLAINNNNN WHY HE LOST HP BROTHERRRR!!!!

enemy pov: https://www.tiktok.com/@sinistreams/video/7608639957950942486?is_from_webapp=1&sender_device=pc&web_id=7599320536765957654