Fission reactors are ran by pulling rods out just enough to keep the system at a state of equilibrium. If one of rods accidentally goes in, for any reason, the nuclear chain reaction therefore heat generation will slowly reduce. If there was also an automatic system that wasn't aware of that rod going in, it wouldn't be so weird that it will try to fight the fire suddenly dying down.

You should write them an email suggesting they try to prevent unintended rod drops