That would be the implication in the "no negro dialect" portion of his statement. Quit being so deliberately obtuse. Light hyperbole as sarcasm is acceptable in any conversation, even here.
That is what you pretend to assume based on his comments. You, however are pretending to not know his meaning by "negro dialect". Everyone on the planet knows what he ment.
If I said that Jane Fonda does not speak with a "Southern Dialect" you would not assume that I was saying that ALL Southerners speak with a Southern Dialect", and you would know exactly what I was talking about when I said "southern dialect"!