To summarise what Sorle said, you are both "friends" so him killing you may just be banter.
But, if you were someone random that Mystic RDM'd then I would understand this report, but paired with the fact you didn't make an F1 or attempt to get Mystic punished in a way seems strange to me.

Rather than wasting your own time you could of made an F1 and dealt with it in-game (and the fact you didn't makes me think theres something that provoked you into making this later on)

To summarise what Sorle said, you are both "friends" so him killing you may just be banter. But, if you were someone random that Mystic RDM'd then I would understand this report, but paired with the fact you didn't make an F1 or attempt to get Mystic punished in a way seems strange to me. Rather than wasting your own time you could of made an F1 and dealt with it in-game (and the fact you didn't makes me think theres something that provoked you into making this later on)