It's a story. Bill Gates said it was because Kildall was flying but neglected to mention he was flying to deliver software to a customer. He thought the person who normally negotiated deals, his wife, would handle the IBM deal. She was advised by their attorney not to sign a non-disclosure. The same lawyer also advised not to sue after Kildall found that Gates had sold IBM a program which was clearly a rip off of Kildall's CP/M (the first 24 function calls were identical LOL). The moral of the story seems to be to have a good lawyer.