That's the same as a deeply nested data structure. A product type. It's not exclusively an OOP concept but it could be to someone who hasn't really delineated the concept of what OOP is.

What I mean by OOP is the smallest unit of programming being an Object with mutating data. These objects are basically combinations of mutable data and methods tied together into entities. Imagine a graph of a bunch of mini-programs with mutating state, moving around, getting injected into one another and talking to one another. This is OOP.

This is opposed to another style of programming where data flows through pipelines from input to output rather then a bunch of entities messaging each other and changing each others state. Both Rust and Go are moving away from this OOP paradigm of programming by putting less emphasis on OOP based syntax.