Positrons don’t move backwards in time in any physical sense. Their mathematical representation is like an electron with a negative time coordinate but this is physically dubious because it fails in curved spacetimes. Electron-positron pairs are entangled because they are correlated by the process that created the pair. Entanglement is just a correlation, not some magical link.
Entanglement is more than just a classical correlation though - it’s specifically the kind where the quantum states can’t be described independently, which is why Bell’s inequalites get violated and why Einstein called it “spooky action at a distanc”.
It’s stronger than a classical one, yes. But Einstein’s description is mocking the idea of entanglement as an active link that allows distant states to be changed by local actions.