I believe he said "arrant" nonsense. Completely different thing. I think.
Arrant means extreme or unmitigated.
Errant means straying from a proper course.
You can plug either one in and still understand the meaning of the sentence. They are, after all, related terms:
They are different (regardless of etymology), but in this case it's a difference without a distinction. In either case, we know we are not speaking of a flattering or benign form of nonsense.
Technically speaking, "arrant" would be the more accepted/recognizable way to deploy this phrase, but what we have here is much less a violation of understanding and much more a simple "gotcha!". Since the meaning is still plain, however, the question (for what it is worth) still stands as a challenge.