Here is my friends video .
First what happened was a gas bomb exploded under his feet which he didnt manage to record but started recording right after and you can see the gas where it got triggered .
Second another bomb exploded but didnt kill him
And finally third bomb exploded also taking about 4 seconds to explode after the first time hearing it which shouldnt be a thing if it was thrown it should less much shorter.

There is another video my friend made , he returned to the location and had several weird things happen to him , from a small gas attack right under his feet to the grenade spawning under him just like it did for me , he will upload the video later.

its hard to see but here is the grenade position and where it rolled , it was quite visible.

I would also like to add that the fuse timer of a grenade is the same amount of time as that grenade took to explode after i first heard it, so either the guy that threw the grenade was in front of that hay bale the entire time and killed himself in the process or they just hacked and pasted in a grenade next to me, because if he threw the grenade the fuse timer after i first heard it would be much shorter then 4 seconds