I dunno; I think the bottom line of this page is that functional programming is a set of approaches for solving problems, and some of those approaches can be done in Swift.
Haven't read the article yet, but the problem I find with this attitude generally is that the constraints found in FP are what I find valuable, and what are usually missing from languages which support functional approaches.
My take was that you can solve problems by breaking things down. In functional programming you do so with functions. In Swift you can do so with types.