The headline here seems to be exaggerated, but it’s probably a real issue: there must be only so many optimal places for wind farms.
Placement doesn’t need to be “optimal” to be profitable.
Nitpick: It is either Belgium and the Netherlands or Belgians and Dutch. I would favour the former.
“Let me make you a present of song as the Belgians steal wind and are gone. While Dutchmen with windmills are grinding their teeth and the nursery rhyme winds along”
I agree. I would find “Belgium and Holland” acceptable because in English (American English, at least), Holland is a metonym for The Netherlands.
Is that the case or is it just ignorance?
At least technically “Holland” consists of two regions of the Netherlands (which happens to be where most of the population live).
A lot of Brits, especially the Scots and Welsh get upset when people (usually Americans) refer to England and Britain as metonyms. I would not be surprised if it is the same wih the Dutch if someone refers to “Holland” but actually means “The Netherlands”
There is no question that Americans use it that way. Whether it is a metonym or plain ignorance is not clear. Recall that Wagner seemed to use it that way.
I’ve never understood why Belgium even exists. Half of it should be in the Netherlands and half in France.
It was created as the neutral zone between two powers. Which is why it was so significant the Germany went through it in WWI.
The reason the Earth has been shunned for so long is also due to a language problem. On Earth, Belgium refers to a small country. Throughout the rest of the galaxy, Belgium is the most unspeakably rude word there is. - The Hitchhiker’s Guide to the Galaxy
It’s not just America, tons of places both English-speaking and not use a term equivalent to “Holland” for Netherlands or e.g. in Japanese the normal word for UK comes from England. It’s an example of synecdoche.
Northern Ireland unionists/loyalists like to be called “British” even though they’re the only ones to not live on the island of Britain.
“Britain” is frequently uses as a synonym for the United Kingdom, and “America” for the USA, so it’s not as though “Holland” for the Netherlands is without precedent.
Indeed, you could argue that “the Netherlands” is itself another example, since the country of that name includes only a part of the Low Countries.
Indeed, going right back - wars of the Spanish and Austrian Successions (or rather, France vs. Everyone Else). Such that it got the nickname “The Cockpit of Europe”.
And virtually no-one who actually lives there wants to become Dutch or French.
Now when I think of Belgium, it’s not gin/beer, Jacques Brel, Front 242, Tintin, or Manneken Pis that first come to mind, it is that they are the baddest of asses in all of Europe according to Caesar, which is why comments like this
make me sad.
Caesar was a long time ago. Perhaps they’ve gone soft. 
Um … to actually get back to the question posed in the OT, the headline as posted is absurd. There is a massive amount of moving air, and only a teeny-tiny amount of it passes through the blades of the windmills. To imply that Belgium is somehow detracting from the wind power of the Netherlands is ridiculous.
Wind shadow is a real thing, turbine placement make a huge difference in the output of a wind farm. The further you are “behind” the other wind farm the the less the effect so can still be significant.
The article claims Dutch wind farms would generate 3% more if there were no wind farms in Belgian waters and I would need concrete evidence to show that is not the case it seems reasonable to me.