That doesn’t appear to be true; on Tesla’s site, the delivery estimate doesn’t change if you add the FSD option. Unless you’re saying it’s an undocumented policy?
They're claiming that the FSD equipped Tesla waitlist is resolved before the non-FSD waitlist. It seems trivial to verify, but it is possible that FSD cars are shipped faster without It being noticed. Maybe by shipping FSD cars at something like twice the rate they are ordered.