He's telling this to New Yorkers, who live in the densest city in the country, and Brooklynites, who live in generally low-rise but still quite dense neighborhoods.
And he's ignoring the fact that Atlantic Yards would be way more dense than Europe. The Observer's Matthew Schuerman last year calculated that the density at Atlantic Yards would be "between 436,363 and 523,636 people per square mile." (Actually, the lower figure is probably a little high by now, given slight cuts in the residential density.)
That number would be nearly double that of the densest census tract in the country, at 229,713 residents per square mile.
And what does Paris, the densest city in Europe, look like? A 1999 statistic says 63,298 residents per square mile. Another stat from Britannica (also apparently 1999) says similarly. The core of Paris is low-rise; the "extreme density" of Paris occurs in the high-rise suburban towers for the poor, the locus of social dysfunction.
That doesn't mean that high-rise mostly luxury housing in Brooklyn would reap the same result; it just means that Olin isn't offering a meaningful comparison. Atlantic Yards is an experiment, in the words of the Park Slope Civic Council, "a new urban form, however, more likely analogous to a spaceship landing in a field than a unifying element in the community."