What a name for land that's never more than 200 m high! But you can understand it:
the park occupies part of the watershed separating the country's two main hydrographic basins: the Escaut, via the Haine, and the Meuse, via the Sambre on its French stretch.

And as the Haine, at the Franco-Belgian border, is at an altitude of 16 m, this name, "Hauts-Pays", the high country, can easily be understood. It isn't just a tall story! Especially as the morphology of this region, or micro-region, is of the Ardennes type.