Understable if you're North American, where 'Scottish' is all I really hear. But it is common in the UK, for example 'Scots law' for the legal system in Scotland.
I'm from the UK. Scots as plural is normal. This seems to be singular i.e. The Scottish mayor -> The Scots mayor.
Isn't it singular in e.g. 'Scots law'?
I believe it is still a plural use of Scots i.e. The law of the Scots. "Scots mayor" is in this case is not referring a mayor of Scotland but an individual who is Scottish and happens to be a major. Just seems off. But the writer is German so no worries.
And I'm not trying to be a Scots Inquisition, just interested in language usage :-)
Or a Scotch Inquisition - which is what happens to you if you put Coca Cola in a malt.