One example is integer ranges; they'd be a runtime check in Rust right now. We'll get there. That said, in general, Rust's type safety stuff is fairly powerful, and IIRC has some things that Ada does not.

I do think your parent isn't fully right about the relationship though, as first they call Rust a "subset" of Ada's guarantees, but then say that Ada doesn't go so far as Rust in some places. In general, when discussing language semantics, I see them as more of a large overlap with some differences on each side, rather than one being a subset of the other.

first thing that comes to mind are bounds on integer subtypes. classic example is to declare an array to be indexed with such a type, then all out-of-bounds errors can be checked at compile time.

As as been mentioned, integer bounds for one. Using aspects in Ada will also let you provide other assurances (at compile time or runtime, depending).

Additionally, the "newtype" in Ada is far easier to work with. The new type inherits the operations of the parent type. When it comes to this sort of thing, it needs to be as simple and easy as possible or it just doesn't get done consistently.