Using edge cases in the syntax to construct an API with unusual calling conventions is not "writing a DSL." Unless you build a compiler/translator for it, it is not a "DSL," it is plain-old Ruby, happily accepted by any conforming Ruby implementation--nothing more.
After their pretentiousness, their arrogance, and their vociferous obnoxiousness, I find their misuse of this once-widely understood term to be their most annoying attribute. It seems like not a day goes by without some eager Ruby programmer hacking together yet another block-based API that kind of, sort of looks like Smalltalk if you squint enough, uploading it to GitHub or some similar site, and then slapping the "DSL" label on it, because Ruby, apparently, is just too cool and powerful a language to have mere "libraries" or "APIs."