How do Mahayana and Vajrayana Buddhists make sense of Maitreya's prophecy?

How do Mayahana and Vajrayana Buddhists make sense of Maiterya's prophecy? I know for a fact that some e.g. son masters claimed to have achieved anuttara samyak sambodhi, and that some Vajrayana monks have taught Buddhahood in this very body. But if Maitreya is the *next* Buddha, how can that be, given he's still not arrived, and is in the tusita heaven? Are there different kinds of perfect enlightenment, and the above realisations are in some way lesser (or more?) than Maiterya's?