He was talking about "sensory keys" but the other person thought it was "requestor's keys"? That can't be it - because it's implied the other person heard the term "sensory".
Can someone explain?
(I must refrain from being very snarky and say that maybe the author is not very good at making points. Oops.)
Their collaborator notes that another kind of key, a "requester's key", cannot be distinguished just by the contents of the key itself; it's more about the context in which the key is used. The collaborator notes that "sensory key" could very well be the same kind of thing, if you don't already know any better. The author was surprised at how implicitly this knowledge was in their mind. They had attributed this feature to adjectives in general, not realizing the subtlety.
A sensory key was a kind of transitive attenuator: it's like a read-only reference to an object such that if you use it to fetch a property from the object, the reference to the property that you get back is also a sensory key. (This is my understanding but I may be confused; I've only read about this OS.)
I'm pretty sure your memory of sensory keys is correct, but I haven't run KeyKOS either.
Still not sure what it means either
Edit: I realise this might be an unfair criticism since this is the author's private blog, and may expect readers to be very familiar with the topics he talks about. Hackernews is not likely not his intended audience, and the unrelated title of "Category Theory" does not help either.