The story about volumetric lights and stencil shadows is rather messy.
Initially, we did not force lights with volumetrics from stencil to shadows.
As the result, with stencil shadows volumetrics simply passed through all obstacles. And several mappers were disappointed by that, saying that volumetrics leaking through stuff has bad consequences for gameplay.
Then we changed the behavior: if player uses stencil shadows, then volumetrics are simply disabled.
But since it many cases (especially where old-school transparent geometry was used) shadows are not necessary, we added a way for a mapper to mark volumetric light as "using shadows in volumetrics not required". As the result, mapper could make some volumetrics work even with stencil shadows. Of course, this markup is not very popular, but the particular light that you found most likely has it.
Then after 2.10 we implemented a force-switch from stencil shadows to shadow maps for the lights with volumetrics.
At this moment, the markup is probably not necessary.
The cvar "r_volumetricEnable 0" simply removes all kind of volumetrics without second thought.
So in this case volumetric light was used, but it worked with stencil shadows because mapper allowed it drop shadows completely.