What I think he's referring to is that you cannot compose new entities that consist of a different mixture of data. I cannot create a ProjectileWeapon that also plays audio, without changing the class to also inherit from an audio node type.
In Godot, you could create a ProjectileWeapon and then add a sub node that plays audio. I don't think that Godot's design limits what you can do at all, there's just a different way of doing the same thing.
Sure you can solve it by basically adding more objects to the world. That's not different from any other engine, but littering your scene graph with nodes because the alternative is inheriting from more things really isn't good.
As much as godot wants to claim their nodes are lightweight, ending up with so many redundant tramsforms, vtables and more (see their Node3D class) just shows how inflexible it is. Again in engines like Unity you can take the exact same approach, they just allow you to author entities without this redundancy.
To add: the blog specifically mentions that using inheritance is used for better re-use, but the need for having this composition through nodes would take that away. I know this might not be your specific point, but it ironically makes it seem they don't see this as an alternative.
