It both is and isn't true. Having cleared that up, I'll elaborate a bit.
Changsha has been reported to have survived 4F during a very short freeze followed by a rapid warmup- I believe that was in Texas, though memory may fail me.
During prolonged freezes, like 140 consecutive hours below freezing, Changsha' will normally be killed around 12F, even on Flying Dragon (FD) rootstocks. This is what I've observed here in the Portland Oregon area.
However, there is certain variance in the cold hardiness of the seedlings, and some can survive lower temperatures. I have one such seedling- the sole survivor of a 140 consecutive hours below freezing with lows around 11F. Later I grafted it onto a FD rootstock and the graft subsequently survived 200+ consecutive hours below freezing with lows of 8F in Jaunuary 2017, even as the original seedling died when it's roots froze.
So, greater hardiness is possible, and is enhanced with grafting on certain rootstocks.
Also, Changsha's in the south, SE , Texas, etc, will be unlikely to see the long extended freezes such as occur in the PNW, so will be much more likely to survive very low Temperatures.
