If there is more than one page of results when doing a query with the MediaWiki API, wikibase:apiOrdinal resets for each page.
This query, for example, returns 10 rows with ?num set to 0:
SELECT * WHERE { SERVICE wikibase:mwapi { bd:serviceParam wikibase:api "Search" . bd:serviceParam wikibase:endpoint "www.wikidata.org" . bd:serviceParam mwapi:srsearch "test" . ?title wikibase:apiOutput mwapi:title . ?num wikibase:apiOrdinal true . } } order by ?num limit 10