[2020] How i died in 1 frame?

It's hard to make out the audio, but it looks like the person shooting at you while prone was using a long-range rifle of some sort. You were also shot in the head, which depending on the server's config settings (and the weapon) can result in an instant kill.

The person that was standing was using an automatic rifle. They hit you first which knocked you down to the 63%. It seems that their friend (the prone person) got the actual kill on you.