When he means is small cars (hatchbacks, superminis) are getting bigger and bigger, a 3-series BMW is now much bigger than the one from the 80s.

The truth is European cars actually tend to be faster than US cars, they are more finely tuned and get more power out an engine. American cars may be bigger but they aren't exactly better, but our cars are more expensive, US cars are dirt cheap for their size.

A little example:

Sports Sedans:

Chevrolet Impala SS 5.3L V8: 303BHP

Mercedes-Benz E55 AMG 5.4L V8: 469BHP

BMW M5 5.0L V10: 500BHP

Luxury Cars:

Cadillac DTS 4.6L V8: 292BHP

Lincoln Town Car 4.6L V8: 239BHP

Jaguar XJ8 4.2L V8 Supercharged: 390BHP

Mercedes-Benz S450 4.6L V8: 335BHP

Maybe the American sedan I've picked aren't the best examples but I doubt any American sedan is as fast as the new M5.