I remind you all of the original ratings conversion...
2500-2650 USATT player = 700-300 ITTF world ranking.
2350-2450 USATT player = 1100-750 ITTF world ranking
You also don't forget a lifetime of training simply because you are working as an accountant for a few years!
I can't believe that ratings conversion is anywhere near correct. If it were then the ITTF list is pretty useless for ranking players below 400 or so. God knows how many unknown 2500-2600 players are in China alone (imagine how many 2350 players there would be!). If some players of the sub-2500 US ratings standard sneak into that ITTF range that would presumably be due to so many strong players not playing in ITTF ranked tourneys.
The most recent clips of Ning show he is definitely very rusty. If you play the physical FH dominant game he plays it can initially take a bit of time to get back into shape but I agree that he would never lose the class he gained through all of his training. I looked at the older clip of him and he is a very strong player indeed. He reminds me a lot of Kim Taek Soo - great footwork and a very powerful FH. Based on the earlier clip I would guess he was at least 2550-2600 but I wouldn't be surprised if he were comfortably higher.