The example lacks functions / flow-control statements (ok, apart from "import if not defined", but it's more of a default value than a branch) / references to other elements. It's pretty much key-value dictionary. Not sure how you got an impression of Turing-complete DSL from that, since it would require at least one of them.
The Nix expression language has branches and functions (including recursive functions). It is Turing complete, and it probably is necessary for its charter.
OP said it "looks like" a Turing complete DSL just from the example. Regardless of what extra functionality the actually is, the examples didn't suggest it.