It's far more than that. The OP said "you know exactly what" - and the comment disproved that, by not "knowing exactly what". Also, how is the comment supposed to refute a negative? A negative that wasn't even a claim to begin with but rather a vague gesture towards some conspiracy (?).

And I am refuting the refutation by "knowing exactly what". Turtles all the way down.

Do you see how silly this is yet? The comment you are defending is - logically - about as valid as not saying anything at all, which is exactly what they told the OP to do.

How can you offer a counter example to such a vague claim?

With a specific claim demonstrating a contrary phenomenon, one would think. "Vague claims" aren't some rhetorical ace-in-the-hole. They can be argued against, presumably better than "you're wrong, and you should feel bad."