Rejected at the final round with 'not a culture add' and no other feedback. What does that even mean?

Got the email after a loop I thought went well. The recruiter said the panel 'didn't feel it was a culture add' and that was the whole message.

I've searched the phrase and mostly found people saying it's code for something vague. Has anyone gotten a more specific version out of a recruiter? Or should I stop reading into it and keep applying?