One way to see it is that a type has a given methods located in a given namespace in the nominal type system.

A nominal type system doesn't necessarily enforce semantics either.

It just enforces the location of a method definition.

Seen that way, because the relation is dual, one could indeed claim that a structural interface is a nominal interface where the name constraint is elided.

But just as in subtyping, one less constraint also means bigger set.

Of course if one were to decide that an object satisfying a nominal interface doesn't satisfy the structural interface obtained by ignoring the namespace, then I'd agree as well, these concepts would be disjoint.

I don't think they are though but I don't know of a language that ever mixed both either.