I'm sure that when they bombed that town someone was in the planes counting how many German soldiers were there at the time.
Maybe they were tipped off and evacuated before the bombers got there. It is a french town after all.
BTW, the second atomic bomb used on Japan justified the first one. The towns where they were used were rebuilt and thousands of Japanese live there. I know this because I've been to both of these towns. So the contamination wasn't as bad as you think.