I dont think it has to do with any bears or explosives sorry that's
The truth is Dida is a secret agent who went to the future and saw the horrors of WWIII and the only way to prevent that was to fell down in that moment( to prevent disturbing the air flow, ya u guessed right its the butterfly effect)
But when he went back to the future nothing changed, he realized when he fell down he damaged the grass (which reversed the whole thing and put the dilemma in motion again)
So he went and sacrificed himself by getting injured on the bench roud: and saved the world
I just think that Billy's "probably" regarding his theory is a bit modest. I would say that it's almost certain or a proven fact that Dida's collapsed onto the ground because he's an experienced hunter and has been told repeatedly to play dead in the event that he's attacked.