I recently tested the troll's aoe (with club) against a pig that i aggro'd into the black forest. Despite numerous ground attacks (with his club) the pig sustained no damage despite being right there in the mix (neither did any of the greydwarfs and greylings).

By indirect damage I was thinking falling tree's perhaps. Here you can see the troll has already broken up a tree (logs) and hit the ground (stones) yet the boar is unaffected:

https://steamcommunity.com/sharedfiles/filedetails/?id=2774199943