If they state it runs more efficient and they redesigned the stator and the rotor they probably use thicker wires for the stator coils which means it can take more amps than M620 and be more powerful with aftermarket controllers without overheating.
Increasing torque and reducing RPM without...
If that Bafang gearhub can hold 250NM torque then they also got the Kindernay killer. Especially with that maximum gear ratio (over 3) bigger than Kindernay VII maximum gear ratio (about 2) that thing can go crazy fast, faster than any drivetrain on the market.
But for some reason the Q-factor of those crank arms for fat bike and regular bike is the same (8) while fat bike should have bigger Q-factor. There is something wrong here.