According to the story Ernie told about their meeting, Fokker was having some trouble with tuning the BMW engine and his mechanics could not fix it. He called BMW to "send your best man" to come and make it work. When Ernie showed up, Fokker began giving him a hard time, saying that they had sent "a kid." Ernie stood his ground and asked simply for an hour to work on the problem. If he could not fix it within that time, he would just leave. Ernie was able to fix the problem and Fokker was satisfied.
From the documentation we have, it is likely that Ernie was sent to Netherlands to work with Fokker. Ernie had a souvenir booklet from Amsterdam, and part of the Fokker story was recorded during remarks Ernie gave at the Bavarian Club, in Philadelphia, on his 88th birthday.
Here is what we know from all of our sources: Ernie was employed by BMW until April 14, 1920, even though BMW was basically shut down in late October 1918 and their stock of engines in Munich was destroyed. At that time, the BMW IIIa engine was the only product that BMW made, so before they were able to diversify their product line, they riffed 90% of their 2,000-man workforce and finally went out of business, selling off their divisions, in 1922. It seems likely that after the War, Ernie was sent from BMW in Munich to Netherlands to work with Fokker.
Fokker needed Ernie because the BMW IIIa engine that had been working just fine in Germany would not work with the Dutch fuel. According to what Ernie said in his remarks to the Bavarian Club, the German gasoline was of an inferior grade, so when the engine was brought to Holland and given better fuel, it would not work properly.
As an aside, Fokker was not a great deal older than Ernie and he had taken quite a bit of guff from the German military because of his young age. According to one story, when Fokker first demonstrated his synchronized machine gun, officers watching declared that they doubted that Anthony could have invented it, saying more-or-less: "Did you invent this yourself, Herr Fokker, or was it your father?" This treatment he received may have suggested to Fokker a way of dealing with this other boy-genius who showed up when he called for a mechanic.
Finally, it is important to note that Anthony Fokker was widely known as "The Flying Dutchman" long before Ernie was given that nickname.
☞ photo of Anthony Fokker -- EBC