To me implied ment something in a episode, not BTS stuff.
That’s true; there’s nothing I can recall in TNG proper that overtly states that Betazoids weren’t members of the Federation even as far back as TOS. But “Betazoid” is still a TNG reference, not a TOS reference.
And Deanna’s father was human, not Betazoid. For all we know, he could have married Lwaxana before Betazed became a Federation member.