So the way the BFG seemed to work in the computer game doom 2 was that after it hit a target every target that the character you control could see took damage

It did not actually explode and damage things near the target that it hit like a rocket launcher

A rocket launcher could damage targets that you can not see but a BFG could not

A BFG could damage targets far away from the target hit by the explosion but a rocket launcher could not

At least that is how I remember it