The Insight book is a giant pice of crap.
Look a this for insanity. Under Rainbow
Nevertheless, this is the first mention of a rainbow, and if a rainbow had been seen earlier, there would have been no real force in God’s making it an outstanding sign of his covenant. It would have been commonplace, and not a significant marker of a change, of something new.
The Bible does not describe the degree of clarity of the atmosphere just prior to the Flood. But apparently atmospheric conditions were such that, until a change came about when “the floodgates of the heavens were opened” (Ge 7:11), no others before Noah and his family had seen a rainbow. Even today, atmospheric conditions affect whether a rainbow can be seen or not.