Did I kill my brother with a bug or an extremely lucky shot?

I was playing Quake 2 with my brother on the edge map. I had run from weapon to weapon finding they were all gone. Finally, I was able to pick up a super shotgun and some shells and made it into the outside room where the railgun pool was.

My brother came out on that ledge with the rocket launcher. He fired his rocket launcher and apparently at the exact same moment, I fired my shotgun in a desperate attempt to cause some damage before I was gibbed.

Imagine both of our amazement, my delight, and his dismay when the very next thing that happened was his rocket exploded right in his face.

Naturally he went on to seek his own vengeance on me, but the experience has stuck with me for all these years.

Was it a bug or a lucky shot?