The general dosimeters available at Chernobyl could only read up to 3.6 Roentgen, so they took that value and said “hey, that’s not a too bad a level of radiation” without realizing (or putting in their due diligence) that the true reading was over 15,000. And the head operator and architect of the disaster (dyatlov) kept using 3.6 as the proof that everything is alright and just a minor setback even though the only higher range dosimeter that was available immediately fried itself

Watch the show Chernobyl, it’s worth it

I was curious too. This is my best guess,

https://en.wikipedia.org/wiki/Chernobyl_disaster

The reactor crew could ascertain only that the radiation levels were somewhere above 0.001 R/s (3.6 R/h), while the true levels were vastly higher in some areas.

Because of inaccurate low readings, reactor crew chief Aleksandr Akimov assumed that the reactor was intact. The evidence of pieces of graphite and reactor fuel lying around the building was ignored, and the readings of another dosimeter brought in by 04:30 were dismissed under the assumption that the new dosimeter must have been defective.

Note the name Akimov in the post.

He’s delusional, take him to the Infirmary