This is Common Lisp, which is multi–paradigm on purpose. You can write purely function code if you want, or go completely object oriented, or just write in a very straight forward procedural style. There are benefits to all of them, so the language designers decided not to force people into any one style. Personally I prefer code that is mostly procedural with a fair amount of functional code mixed in.

In Common Lisp you have the option of using CLOS which is a wonderfully flexible and customisable object system:

https://lispcookbook.github.io/cl-cookbook/clos.html

Lisp is composable. Everything is possible. Functional programming is one of many paradigms and many are common in it.

CLOS is an abstraction layer to enable OOP. It has long been a workhorse in industry. If a programmer wants something in lisp, he can make it.

The textbook sicp (not common lisp, but another dialect) involves building different interpreters to enable differing behavior. A lot of these are configurable or availible through libraries in common lisp. You have near infinite power with it! (Making a unique dsl for your specific problem case, e.g. with macros, is common with racket (my favorite lisp dialect.))

In the 80s and 90s when OOP was gestating and emerging, a lot of experiments and projects in thst direction were made in lisp (in production etc.) just as a lot of quantum computing research is done in lisp today. Indeed, in 1994 lisp became the first standardized OOP language. In the 60s, object modeling was first done - with lisp. The 70s already saw significant research in the area, before being used in industry in the 80s.

For functional only, you have to go to haskell.

It’s written in a very OCD style of coding, which I love. Definitely one of the most readable pieces of code I’ve seen in a while.

Lisp is not very functional at all.