Continents are messy, because landmass on Earth is messy, it's contiguous where it looks like it isn't and so on.

A more surprising thing (at least IMHO) is that different countries have different definitions of... mountains.

I'm not a geologist but if we can trust Wikipedia (https://en.wikipedia.org/wiki/Mountain):

- in the UK mountains are at least 2,000 feet high

- according to a UN program, mountain environments include places with "Elevation between 300 and 1,000 m (984 and 3,281 ft), with a 300 m (984 ft) elevation range within 7 km (4.3 mi)"

- according to the US Geographical Survey (USGS), there is no official definition of mountain