This is trivial to look up. They do not in fact own the trademark "open source". Apparently I can't share a direct link to uspto search results, but you can sea

This is trivial to look up. They do not in fact own the trademark "open source". Apparently I can't share a direct link to uspto search results, but you can search by owner and see they have 7 trademarks, none of which are for the term "open source". https://tmsearch.uspto.gov/search/search-results https://tmsearch.uspto.gov/search/search-results