The article has a picture of the dotted line. It doesn’t appear to be a contour map at all.

The article doesn’t mention OSM at all

Downvoted by people not used to reading topographic maps I guess ;) In all seriousness though, not sure why it's being downvoted. Perhaps we are just misunderstanding each other? That's how topographic maps work so I'm asking if that was not the case here. Surely even the online topographic maps come with a legend?

I’m used to OS maps in the U.K., and yes, contours are quite obvious, and map reading is a basic skill learnt about age 8.

However there’s no guarentee a give OSM render will show contours, footpaths, and different rights of way, in the same way as OS, or have a legend.