It's just an observation rather than a judgment, and -- again from a type-theoretic perspective -- it's true. It's nothing to be offended about!
Note that if you were to write a type checker for a unityped language, then every program would trivially type check. So, while technically accurate, the notion of a language being "unityped" is not very useful. It's more of an intellectual curiosity than anything.
That said, it's a completely true point in the notion of "static-types-as-type-theory-defines-them" that dynamic typing is a mode of use of static typing which is completely captured in large (potentially infinite/anonymous) sums. Doing this gives dynamic languages a rich calculus.
Refusing to doesn't strip them of that calculus, it just declares that you're either not willing to use it or not willing to admit you're using it. Both of which are fine by me, but occasionally treated pejoratively because... well, it's not quite clear why you would do such a thing. There's benefit with no cost.
Then sometimes people extend this to a lack of clarity about why you don't adopt richer types. Here, at least, there's a clear line to cross as you begin to have to pay.
The "Church view" and "Curry view" are psychological—the Wikipedia article even stresses this! So, sure, you can take whatever view you like.
But at the end of the day type systems satisfy theories. Or they don't. That satisfaction/proof is an essential detail extrinsic to your Churchiness or Curritude.
The core.typed user guide and it uses the same definition of type that I'm familiar with from "Church" type theory. It even makes the same observation that Clojure is unityped! It seems to me that core.typed does not use a "different" type theory at all. Rather, it is a testament to the great extensibility of the Lisps that a type system can be bolted on as a library. Perhaps unfortunately, most languages are not so flexible.
P.S.: I re-read Harper's original unitype article, and it does seem pretty combative. I still don't consider the term pejorative myself. I dislike the term, but because of its lack of utility above any other reason.