If we must follow this kind of speculation, then here is a close up photo of the NDH 30 driver by
@Vitaliy Belz from his early posts in the NDH 30 thread:
and one of the HD 490 Pro from Reddit:
We can see that out of the 3 printed numbers on the membranes, 2 are clearly different and the last might be similar. We cannot be sure if the drivers (or the membranes) are identical judging from the printed numbers but if they are then it's a good thing for the HD-490 Pro.
I am sure though that much more strict tolerances of parts are used for the NDH 30 to achieve that impressively low THD of 0,03% compared to the 0,2% of the HD-490 Pro. I don't know if these values are really audible but the NDH 30 sounds considerably more undistorted and transparent than, say, the HD-650 which boasts a THD of 0,05%.