It could be laid out in a binding contract for the purchase of .org that the PE firm is prevented from reoffering a name renewal above the rate they previously

It could be laid out in a binding contract for the purchase of .org that the PE firm is prevented from reoffering a name renewal above the rate they previously offered it and the agreed adjustment - it just appears that isn't actually contractually laid out anywhere and is simply a PR statement. Contract law certainly isn't something to trivially walk into, but there are ways this could have been done.