[ars]

> it's an unfalsifable claim, so it should be ignored in a context of formal logic

The claim might be unfalsifiable, but the question is still valid. Basically you are required to answer the question. If you answer "I can't know" your answer is also unfalsifiable, and no better than theirs.

i.e. your position on this matter is not superior to theirs.

[torben-friis]

Admittance of ignorance is undoubtedly better than a lie, in general.

[ars]

I wrote "I can't know", not "I don't know".

This is a question about the limits on knowledge, not about someone's personal knowledge.

[mensetmanusman]

It’s impossible to say whether it is a lie, because of incompleteness.

[NateEag]

Let's try the more charitable "unjustified certitude" instead of "lie".