Is the ability to evaluate the quality of a performance inextricably linked to complete understanding of the language? Unless Japanese acting is truly incomparable to Western acting in every facet, I don't think it's beyond the abilities of a layman to evaluate a person's acting (though I agree if you actually meant something more along the lines of evaluating Japanese writing). I think that a performance is more than just the words that make up the language, that there are subtleties in inflection and speech patterns that can be observed even by someone with an incomplete understanding of a given language. Were this not true then performances utilizing invented languages (such as ICO) would be inevaluable to everyone, and I don't think that anyone genuinely believes that. I think it's possible to have extremely well-acted performances that grip the gut of the audience, even where the language is complete gibberish.
I'm no linguist, but I've seen very... stilted performances both in languages that I do and do not understand; by that same token, I've seen powerful performances on both sides of the train-tracks that tugged at my very heart-strings.
Read it again; he was saying that scarce anyone here could accurately evaluate the quality of a Japanese dub as good.