I have personally been discarded from a startup without even a phone interview, because of "not being a cultural fit to the company". What makes it more absurd

I have personally been discarded from a startup without even a phone interview, because of "not being a cultural fit to the company". What makes it more absurd (if possible, how do you determine "cultural fit" from a CV?) is that the position was remote. What makes it even more absurd is that the company actively used a software I wrote. I deduced that "cultural fit" translated to the fact I was over 35.