Internalism

How do you know the dude isn't willing to accept external verification of his internal truth?

The whole point about the Nietzschean position is that it points to the impossibility of discriminating between descriptions and so-called 'reality' per se. All we can have are more useful, or less useful descriptions according to context. So 'truth" boils down to 'what is considered to be a useful (or good) description'. 'Coherence' amounts to 'goodness of contextual fit'.
Pasting aimed at rhetorically torpedoing one liners concerning 'truth' is fine, provided that the wider implications are fully understood. In this case, I suggest they are not, and that the paster should apply the Nietzchean position to his own fixation with particular paradigms in physics.

Truth cannot be a property of statements by themselves. It's a property of statements in their relation to reality. A true statement is simply a sufficiently correct representation of reality.

All HUMAN language are ambiguous. A single sentence can have several meanings, indeed it can assume a near infinity of possible meanings, by use of metaphores. Take the rather bland and banal sentence: This apple is good! The apple in question can be the one I am eating while saying this (literal meaning) but it can be a metaphor eg for New York -- This (Big) Apple is good. Or I could be ironical, eg if the apple is rotten... You get my drift. This capacity of human languagesvto mean several things is called polysemy.

The point is that sentences, as strings of words, are not true or false per se. Their meaning(s) (or one of their possible meanings) are true or false.