Zach Davis is an Appalachian Trail thru-hiker, author, blogger, and bearded bacon aficionado. His competencies include (and ARE limited to): goal-setting, social media, writing, backpacking, community engagement, and beards.
I agree with Jason, you should definitely give credit to Gladwell. He popularized Moskowitz's story.
There's no downside to citing Gladwell as the person who brought Moskowitz's story to the mainstream. There's potentially a substantial downside for not citing it, as some will likely perceive that you're claiming this as original research.