If you developed the libraries yourself, then you have a point. But if you're using someone else's library, which they maintain, then it seems reasonable to say

If you developed the libraries yourself, then you have a point. But if you're using someone else's library, which they maintain, then it seems reasonable to say your application is pure Swift. Note that there's a difference between saying "my application is pure Swift" and "everything is pure Swift". If you're trying to make an argument about safety (as happens when people talk about writing things in Rust), then having the libraries written in that language is important. If you're just trying to say "this is a modern codebase using the latest tooling and APIs", then all that matters is the code you wrote, and not the pre-existing libraries that you link to.