TL:DR--> Pve damage is applied to the traps when they stick to an agent,causing absurd damage.
While in the dark zone ( i have not tested this on conflict) throwing a shrapnel trap will instantly kill other players,provided said player has 2 or more skill tiers. There are multiple reasons as to why this happens,of which i will explain below.
1.This is due to the ability of the trap to "stick" to enemies if they are within the radius of the trap during activation and will detonate after a short moment,multiple traps can "stick" to the same or multiple targets.
2.However,this does not justify the absurd damage output against other players,considering the fact it will kill you even with a 80% explosive resistence build with 2 million armor when the other player has a full tank build with no skill damage atributes what so ever.
3.This brings us back to the necessity of 2 skill tiers for a one shot,even though the traps barely cause any significant damage at this tier if they are laid on the ground,they will easily kill any player if they stick to their agent, even though there is no damage boost for sticking a trap to an enemy,both in pve or pvp.
4.Obviously none of this makes sense,so why does the trap one shot anyone without good reason? Simple! Because pve damage is being applied to the trap whenever it is stuck to a player. Since the shrapnel's damage starts to get really high at around tier 2 in pve,it makes it impossible to survive the explosions for any agent.
5.From a coding perspective i have no idea how this works so take it with a grain of salt,but whenever the traps stick to and kill an agent it says they killed themselves and no credit is given to the traps owner,though i have no proof of it i theorize that the game is actually applying a debuff to the player instead of explosive damage from the trap,said debuff's damage is calculated on the amount of skill tiers the traps owner posseses.Except that since the game can't show "Tom clancy's the division 2 has eliminated x player" it simply opts for suicide as the cause of death.