I've posted this in a few threads right now:
That site is suspect. The "radiation map" page did not seem to exist before today: https://web.archive.org/web/20220224230609/https://www.savee...
They claim to have "1 million users", and yet only have 22 Twitter followers: https://twitter.com/SaveEcoBot
It smells of a misinformation campaign to me. If there was a spike of radiation at Chernobyl, I'm sure we would very quickly hear about it from more reputable sources.