The animals knew better than humans how quickly actually harmful levels of radiation would recede.
“Well, no. The animals aren’t tuned to radiation any more than we are. It is more likely that they just died off in fewer number as levels receded.”
While I admit using “knowing” about radiation only metaphorically, there is no evidence for your suggestion for the flourishing of flora and fauna in the abandoned Chernoble area. I don’t think anyone researchers have foolproof conclusions on why it is; but the fact remains there is an unexpected abundance of flora and fauna where scientists said would be centuries recovering.