They don't say how/where they measured, so the figures are basically worthless. 65-70 dB(A) seems on the low end of consumer unmanned quadcopters[1], e.g. "Maximum sound pressure level for fast flyover at 15 m height: 62 dB(A)" for a DJI Phantom 2 weighing less than 2kg.

If they managed to get into that range for a vehicle that must weigh many hundreds of times more, I guess that'd be very impressive.

[1] https://www.mdpi.com/1660-4601/18/11/5940