"up to" Those are the magic words. As long as they pay just one author 5cents a word, then they are being honest. You (or I) may not be that author who gets the good rate, but they didn't say the PAY 5cents, just UP TO 5 cents.
Similarly, if you go to the store (at least in Mich and many places in the US) and they have a display saying $1.00 and up, they only need ONE thing in that display that is $1.00. Then it's not false advertising.
=/
(I always HATED being ordered to build displays that were clearly intended to dupe unsuspecting buyers. But ti's legal.)