Bug or intended execution?

[mvgulik]

wasn't it changed in some patch from months ago so that there's a RNG based chance of animal to keep attacking on KO ?

I don't know. A quick search did not turn up anything related, but I would not rule it out.

[smr010]

My friends lured the mammoth away a bit

How far away is "a bit"?

Like 10 tiles more or less.

....or if it's really a powerful, big AoE attack that killed me. Can anyone confirm if it does such damage?

no idea but if you did not have mammoths portrait in top right corner then it's difficult to find other explanation

It was still aggroed onto me, so I did have its portrait in the top right corner. It was not attacking me directly though, nor shot its projectile at me at any point.

[Lalaxx]

or if it's really a powerful, big AoE attack that killed me. Can anyone confirm if it does such damage?

yep. if it stacks enough initiative points it can literally oneshot someone in low armor from like 10 tiles away. He knocked our archer once and we laugh cuz he was like over there shooting arrows and we were tanking mammoth super away from him.