I'm guessing this is set in the new universe created by Pucci before Emporio kills him in 2011/12. Hence, we have Diego "DIO" Brando, when we should have vampire DIO, and a new Zeppeli in 1890. This must be why people are unsure if part 7 & 8 will get anime adaptations since any familiar faces we will see will not be exactly like the people we've known so far.
Effectively the series has been rebooted unless we get merging/cross-overs between the universes we are aware of. However, the people in the prison remembered the previous universe so maybe the same events took place, making this universe completely separate from Pucci's. Hopefully this gets explained later.