These predictions given to various people telling of the future enlightenment and Buddhahood of all these people is referring to the enlightenment attained because of their practice of the Lotus Sutra. The enlightenment of these individuals is not due to their current practices or those practices they have engaged in up to this point. The Buddha is saying basically that they all arrived at this point, in time and faith, by various means but from this point forward their path to Buddhahood is based solely on the single Buddha practices in the Lotus Sutra. While there were a variety of ways to practice to get to this point there is only one practice going forward.