This was not an FBI underground base.
Lacking the means to clean up radiation, the consequence of having only one containment container was that radiation energy was arbitrarily released within the forest.
This led to the subsequent events.
It also let Brian learn about the origins of the tumor monster.
That guy was clearly an example of cellular self-destruction: his entire cells mutated into cancer-like cells, began proliferating wildly and swelling, causing his external form to undergo irregular changes, eventually turning into something resembling a melting ice cream person. Moreover, while fighting with the previous little wolf-dog, due to the mutated cells within, he could not draw enough energy and suddenly dropped dead.
If all this was true, the effects of the "Residual Glow Stone Slab" were truly astonishing.
...
Brian couldn't help but look over the contents of the inner box once again.
This time, his focus was on the word "evolution."
