I can say it's not a subtyping relationship because it happens entirely at runtime and my definition of types—the one consistent with what I referred to as Haskell's standard type analysis—does not include runtime dynamics.

If you want to pick a definition of typing which includes runtime information (and referencing RTTI, clearly you do) then we can shift to that vocabulary and talk about whether such an analysis includes a subtyping judgement. I'm not familiar with it.

But it's certainly not consistent with the standard Haskell type analysis. So there shouldn't be any surprise that the vocab doesn't match up.