FWIW I think that's the essence of the complaint here: "is a" can mean various things in various contexts, but Liskov substitution principle and OOP design gene

FWIW I think that's the essence of the complaint here: "is a" can mean various things in various contexts, but Liskov substitution principle and OOP design generally requires it to mean something specific, and using "OOP is a" when you meant another "is a" is an easy trap to fall into, because the language makes it so easy to do. But I don't see why this is a complaint about OOP in general. It's a complaint specifically about inheritance. That said, the claim that integers "are" naturals is mathematically 100% false as well, so the example in the article is also kind of a silly straw man.