The "Matches Natural Search Detection Rules" depends on Adobe Analytics
being able to recognise a referrer as a search engine. You can read more
about this recognition at
https://experienceleague.adobe.com/docs/analytics/components/dimensions/search-engine.html?lang=en.Some
traffic could be coming from Google properties that are not the search
engine, e.g. Google Images, Google My Business, Google Maps, etc. In
such cases, Adobe Analytics would classify them as Referrers instead of
Search Engine...