"Bot has been destroyed" - huh?

Spotted this in a log from a couple of weeks ago, so it's still current. I don't think I've seen this "... and has been destroyed" line before - can anyone tell me what that's about?
Possible factors: acid rainmaker weapon, massive overkill on the final hit (78% total = +54% past SL, according to the score), L0 victim.
--EDIT 1--
Found another one with a L2 taking +58% overkill (single Magnus Hammer attack, 158% damage) but no "destroyed" message. Is it a specific weapon thing, or a L0 thing?
--EDIT 2--
Aaaand another one that matches the first in everything except level and doesn't have "destroyed": whopping +68% overkill, acid rainmaker, destroyed from <25% on second hit; the only difference is it's a L3 bot. So is it something that happens to L0 bots taking massive overkill?
--EDIT 3--
FFS, now I've got a zero-XP bot taking +109% overkill (!!) from a Magnus Hammer and not being destroyed... Is it to do with the weapon? Both bots have 0 STR so no armour involved...
Possible factors: acid rainmaker weapon, massive overkill on the final hit (78% total = +54% past SL, according to the score), L0 victim.
--EDIT 1--
Found another one with a L2 taking +58% overkill (single Magnus Hammer attack, 158% damage) but no "destroyed" message. Is it a specific weapon thing, or a L0 thing?
--EDIT 2--
Aaaand another one that matches the first in everything except level and doesn't have "destroyed": whopping +68% overkill, acid rainmaker, destroyed from <25% on second hit; the only difference is it's a L3 bot. So is it something that happens to L0 bots taking massive overkill?
--EDIT 3--
FFS, now I've got a zero-XP bot taking +109% overkill (!!) from a Magnus Hammer and not being destroyed... Is it to do with the weapon? Both bots have 0 STR so no armour involved...