I don't think that's true. Have you seen how they move cattle in trucks? Maybe more space than a human because they take up more space, but they stacked right next to each other.
Have you seen the commuter trains in some larger European cities, like London, Paris, Brussels (I think)...?
People sometimes aren't just stacked, they're squashed.
India produces some real champions in this sport, the euros don't stand a chance. They have leagues up to "super-dense crush load", 14-16 people per square meter. It's still hard to believe this is possible...