What exactly is the benefit of obfuscating the source language? Your hypothesis that it's written in Scheme is reasonable, but a DSL by any other name is a basket of Lisp macros. It's not a new language, but at the same time, it's kind of a Domain-specific language.
At any rate, I don't think that if it was Scheme that the goal was to obfuscate that it was written in Scheme.