OK, so via Special:LinkSearch you get plenty of results as you link to at https://ru.wikipedia.org/wiki/%D0%A1%D0%BB%D1%83%D0%B6%D0%B5%D0%B1%D0%BD%D0%B0%D1%8F:%D0%9F%D0%BE%D0%B8%D1%81%D0%BA_%D1%81%D1%81%D1%8B%D0%BB%D0%BE%D0%BA/%D1%80%D1%83%D1%81.%D0%B1%D0%B0%D1%88%D0%BA%D0%B8%D1%80%D1%81%D0%BA%D0%B0%D1%8F-%D1%8D%D0%BD%D1%86%D0%B8%D0%BA%D0%BB%D0%BE%D0%BF%D0%B5%D0%B4%D0%B8%D1%8F.%D1%80%D1%84

When we do what I think is the equivalent search via the API I only see one result in namespace 1: https://ru.wikipedia.org/w/api.php?action=query&format=xml&list=exturlusage&euquery=%D1%80%D1%83%D1%81.%D0%B1%D0%B0%D1%88%D0%BA%D0%B8%D1%80%D1%81%D0%BA%D0%B0%D1%8F-%D1%8D%D0%BD%D1%86%D0%B8%D0%BA%D0%BB%D0%BE%D0%BF%D0%B5%D0%B4%D0%B8%D1%8F.%D1%80%D1%84

So I don't understand why the API is giving us different results, I will ask on tech village pump

The one result for the API query was actually an error that was fixed by a purge with forcelinkupdate.

Change 279727 had a related patch set uploaded (by Anomie):
API: Normalize input URL in ApiQueryExtLinksUsage

https://gerrit.wikimedia.org/r/279727

Change 279727 merged by jenkins-bot:
API: Normalize input URL in ApiQueryExtLinksUsage

https://gerrit.wikimedia.org/r/279727