It bothers me more than it should that he calls them "spomeniks", because that's literally just a word meaning "monument" in the local languages.
It's like someone going "did you know American monuments are known as monuments locally?"
It's like someone going "did you know American monuments are known as monuments locally?"
Anyway, if someone visit one of Balkan countries and ask to see spomenik, expect locals to be confused and would not know what exactly you mean.
More seriously, I think you're exactly right about the adopted internet-English meaning of 'spomenik' and the article is right to make a distinction between this particular (and much more interesting) variety and your more generic strictly-regime-sponsored concrete artblob.