I think usually the standard wording for this option would be something like "Reject all non-essential cookies" and they left out the second part of that sentence. I'm not saying it's OK but maybe it's a mistake that was done in good faith.
GP is alluding to the fact that several tracking networks will place their cookies in the "legitimate interest" category, because the rationale is that them making money by monetizing user data is their "legitimate" moneymaking interest.
There's not a lot of good faith in that, and it's arguably not valid according to GDPR.
