What the hell is this out of context statement?. Like of course they are all human, same ancestor. If it is literal causal reset, why PE and CE distinction exist?
Yes, there's leftovers from the Previous Era, but it's clear that humans can't be revived in Hi3. Kallen and Otto's arc proves that. So it's not just 'reviving' these people, it's reversing time (and therefore causality) to the point where they did exist.
'Same ancestor' is a bit misleading, that description is fitting for saying a parent and child have the same ancestor.
The point of the statement is that in this point in time, 50,000 years back from both the PE and CE, both Eras came from the very same humans. Both eras are 50,000 years away from these humans.
The eras only deviate due to pure chance, and of course, the flame chasers.
Also the game made clear that close to the end of PE before Finality nuke, that the Stigma project or whatever it name was, ensure a batch of human with stigma to counter Honkai, goes into statis and waiting to emerge to start a new generation, that why new CE human can have stigma
That was using the Herrscher Core of Ice in the stasis chambers to resist the time rewind. The Cryopods are Divine Keys.
I'm genuinely not sure about the debris left behind by Finality on Earth. It's likely just PIS or Prometheus pulling something that was never expanded on. It is all soulium stuff though, maybe that has something to do with it?
Either way, the general rule is that it IS a causal reset, and the exception (Aca 4 in this case) would be various plotpoints like the flame chasers.
The thing that makes this unclear is that the causal reset was a retcon. The original story intention was the CE was 50,000 years after the PE, yet the devs shifted to there being a reset via the Cocoon. This of course makes plotholes that we're discussing now.