The notion of "Open Source" has an agreed-upon definition, understood widely within the community of software development practice: https://opensource.org/osd
By the same token, "Free Software" has a specific, narrow meaning: https://www.gnu.org/philosophy/free-sw.en.html
What would you tell a person who would peddle you deep-frozen apple juice as "hard cider", because it's technically cider, and is undeniably hard?
(While at it: I must praise the choice of the font on the page, super clean and legible. It's Lexend, freely available from Google Fonts.)