It is a mistake. The bomb does not damage a radius, it damages an area which is quantified by a radius squared. Again, this is high school geometry, not controversial, and maybe there are factors not explained which make this correct in a sense (maybe "damage" is a term of art which varies by the square root of area destroyed? Seems unintuitive, but I'm not an expert in atom bombs or much of anything.)

It's a silly error which in no way undercuts anything in the article afaict, but it annoys because it is very simple and obviously true by unit analysis. I make silly errors too, as we all do, present company excepted. But it does undercut my confidence in the more far difficult journalistic work being done, which I cannot interrogate with my limited mathematical skills and pretty much have to take on faith. To me it speaks to the question of whether I "learned something" or "read some words".

This is a very boring digression and I take full responsibility for making a ticky-tacky point, which I have now I believe fully explained and contextualized.