Connection between zombie virus and radiation in U3 lore

I’ve always wondered why this foreign spies bunker and Silo 22 itself both got infected? Is it due to the direct spread of the zombie virus or due to Silo 22 leak? We have no clear information about this part of lore.

Because the missile failed in silo 22 and spread radiation everywhere, forced an evacuation, got sick, went back and died of radiation and sickness

This is not an explanation cause in such cases the evacuation needs to be quick, and there is no point to come back.

They go to military base
Military base gets overran by zombies
They go back to silo 22 expecting it to not be too terrible, which explains why there’s filters and gasmasks there
People are infected by virus

This is just theorising. And why Coalition bunker (or foreign spies bunker as MoltenMontro confirmed) got infected too?

because rads fucking suck

He’s asking why they were infected, though.

Possibly a group of them went out to get supplies and got infected, then came back to the bunker and unknowingly infected everyone.