My own culture is all about distrusting others and being very selective about what you reveal about yourself and paying close attention to material balance in social interactions so someone else isn't getting more out of the relationship than you. A point that came up last time I was visiting my home country was that my habit of thanking the cashier after finishing my transaction was a glaring giveaway that I was an outsider, and that I should be careful about it to avoid being taken advantage of.
In comparison, American culture has been very freeing, I can typically trust people to not be trying to stab me in the back, I don't have to worry as much about taking advantage of by friends, I can ask people to be honest about me and they will be, and so on.
There are a lot of little pleasantries with strangers that took time to become fluent at, but people you actually know seem to be just as honest as what the author describes the Dutch as being, just with a lot of initial padding like "please don't take this the wrong way".
The example given of being asked to dinner and responding bluntly with "I'm busy tomorrow" doesn't seem that rude to me, but to be fair, I am in a physics and engineering environment, neither groups of people being known for their social smoothness :)