Hi There -
I'm a development editor and literary agent with over ten years experience in the industry. Saw your question and thought I'd chime in.

You can mention the story in your book, yes, but you do need to reference Malcom Gladwell's speech or whomever said it and wherever it came from. It doesn't have to be formal, but something like, "When Malcom Gladwell was speaking at xxx, he told a story about ....." Then after that you'd connect the story to the point you're making or it's possible the story serves to support a claim you made beforehand.

If you're interested in hopping on the phone feel free to reach out.

All the best,
Cynthia