Chances are they are, per capita, importing a lot more than others (haven't looked it up but I'd be surprised if they didn't, happily surprised that is), and if that's the case, "others do it too" (but less of it) doesn't rule out that the nl food surplus is more a form of processing (of other countries agricultural output) than of domestic production, that just hides behind the different classification of imports and exports (one isn't food, the other is). How much agricultural surplus would there still be if they were isolated for a few years?

I think that is mostly flower greenhouses but could be wrong.

No really. The modern greenhouses act as little power plants, burning gas and generate electricity for the grid when demand is high, or act as a sink with electric heat when demand is low.