How a 3 week business trip to the US got reduced to 3 hours
This was somewhat surprising to me, but appears that he was accurately quoted the law.  If you go through the flowchart on the State Department's website for the Visa Waiver Program, which would be my #1 suggestion for someone coming from the Netherlands,For the purpose of the Visa Waiver Program, "business" generally refers to business activities other than the performance of skilled or unskilled labor. Examples of activities that are allowed include:
engaging in international commercial transactions, which do not involve gainful employment in the United States (such as a merchant who takes orders in the U.S. for goods manufactured abroad, or who travels to the U.S. to purchase American-made goods for export from the U.S.);
negotiating contracts;
consulting with business associates; and
participating in scientific, educational, professional or business conventions, conferences, or seminars.The performance of any skilled or unskilled labor - even if it is unpaid - is most always prohibited. This includes performing work in the U.S. as a trainer or consultant.
Activities allowed on the VWP parallel those activities allowed with a standard "B1" category business visa. Please see our B visa information page for more details.Working visas are, as stated, not exactly trivial to get.  (And if you're already at the airport it is too late.)