I am not 100% sure what you are trying to do.
In Unreal Engine, both material and material instance use Material Interface as their common parent class.
In UEFN, both use the parent class “material” therefore you do get a different name.
To understand your issue better and maybe help you on the way:
I guess you want to create a new material from Verse code?
Why are you trying to create a new (material) class? (You cannot in UEFN.)
Try not to create a class when you actually want an object. (your new material/instance)
If you want to create a new material, do it through the editor as it will show up in the material digest.