I agree that they are both deformation, but I would definitely not classify them as the same thing.
Extrusion would dynamically generate geometry from a base mesh (along a spline), thus basically constructing a new mesh. With mesh deformation, especially how it’s usually used (animating rigged characters), the geometry only deforms (positions and maybe normals change) and things like the UV coord for each vertex stays the same.
They could be animate-able (probably not in my (and many other) cases though).
Maybe they can be generalized to a single thing with some parameters, I’m unsure, up to Roblox to figure that out . In my mind they seem completely different, though.
This is an example of how mesh extrusion along a spline is frequently used: