Well, Evans and Vernons books use OOP. And when I was interested in the topic (actually it was event sourcing, which seems to be near 100% married to DDD, if you search online resources), I found only blog postings using OOP.

I found it funny, too, because IMHO event sourcing is fundamentally data driven, so FP would be a more natural fit.

He clearly says on the book that it's written using the tools that most people use, and that this is not a recommendation for the tools in any way.

He also gives a counterexample about implementing it in Prolog.

From experience I've found it easier in FP languages to get right, and have them stand a few years than standard OO without it being a maintenance headache having written a few of them. So yes - I figured the same thing.