They typically mix up parametric polymorphism and ad-hoc polymorphism.
I blame C++'s templates for the confusion. (And Go people's common refusal to look much further, and especially not into academia..)
I don't think that's a fair statement, given Phil Wadler's formal work on generics in Go - "Featherweight Go" (https://arxiv.org/abs/2005.11710) - which is acknowledged here: https://blog.golang.org/generics-next-step
It's good to see that they are taking the likes of Phil Wadler serious. (Perhaps his beard helps?)
> We’d like to thank Philip Wadler and his collaborators for thinking formally about generics in Go and helping us clarify the theoretical aspects of the design.
In the older post at https://blog.golang.org/why-generics you still see them pretty much mix up parametric polymorphism and ad-hoc polymorphism.
Thanks for the link to the paper!