I'm not at all sure the 2m number is correct. My points are that it doesn't include Catalan speakers, and that the number of over-65s in the Occitan-speaking regions places it within the bounds of possibility.

As for INED, there is not much credence to accord to the survey that concluded on 526,000 speakers before correcting that number by 50%. The source quoted ("Qui parle occitan?" (pdf)) outlines the inconsistency of the survey (which left out several Occitan départements, including the one I live in). The sentence before the quote says:

Bref, du point de vue quantitatif, il y a peu à attendre d'une telle enquête.

(In short, from the quantitative point of view, not much can be expected from such a survey)

The article is not the source of the 2m number (which is not discussed on the Talk page). So it's true it's a mystery.