I believe that this claim is neither right or wrong! After researching for articles to backup this claim, I came across this article by New York Post. And in this article it does only give a written response about Taco Bell being the fastest fast food drive thru, but at the end of the article it shows a graph of various different fast food chains and the time it takes to get your food and Chick-Fil-A is at the bottom. But as I continued to research more I found this article by Food & Wine, and they claim the complete opposite opinion about Chick-Fil-A. In this article they don't even mention Taco Bell at all.
Truthfully, I do believe there can be a statistical answer to this claim but in the end I feel it just depends on the location in which your ordering from!