Some more context, from the link:

I consider the claim that 'ought' cannot be derived from 'is' to be a very remarkable claim. It suggests that there something . . . 'oughtness' . . . that is totally distinct and separate from things that exist in the real world . . . 'isness' . . . yet is supposed to have relevance in the real world. It is referred to as a part of the real-world explanations for the movement of real matter through space-time. Yet, we are told, this 'ought' or 'should' that we are making a reference to and that has these owers is something distinct and separate from anything in the world of 'is'.

[...]

My position is that 'ought' is relevant in the real world because 'ought' is a species of 'is', and there is no mystery as to how 'is' can be relevant in the real world.

So, when I put you cannot derive 'ought' from 'is' up against 'ought' can interact with 'is' because it is a species of 'is', and I realize that one of them must be mistaken, it seems far more likely that we will find the error in the first proposition rather than the second. I would be far less surprised by a discovery that 'ought' is relevant to 'is' because 'ought' is a subset of 'is' than that there is a realm of 'ought' separate and distinct from 'is' but still relevant in the world of 'is'.