There are times where in Lisp, OOP makes things so much easier and clearer. The way that Lisp does OOP (should you choose to even use CLOS) is fascinating and comprehensive. But as with everything else in Lisp, style is personal, and you aren't locked in to any particular set of rules in that regard.
But I do get the subtlety whereby Java's implementation (and everything that came thereafter) is what the author is poking at.