I can't remember enough details of the story to be sure, but I would guess it refers to the highlands of the German speaking countries, that is to say the southern rather than northern part of the countries. Official German is usually referred to as Hochdeutsch (High German) because it originated in the Highlands, whereas dialects in the southern lowlands are referred to as Plattdeutsch (Low German). Old English was a dialect of German, by the way.

To add to Phil, we never say "high" to describe a person's height - they are always "tall". Curiously, you can use "high" or "tall" synonymously for a building