One reddit user fit a quadratic curve to the infection rate some time ago and used it to predict the number of infections.
https://old.reddit.com/r/bestof/comments/f0anox/uantimonic_a...
This is how the figures have grown for confirmed cases, i.e. number of positive test results that came back. Not "actual real number of cases", which I'm sure the healthcare professionals and politicians in China are all aware of, as everyone else should be. It's already been clearly recognised that Wuhan/Hubei botched the early part of managing the epidemic, so the discrepancy you point out is pretty expected.
Now granted, the articles are anecdotal and not statistically representative, so there is some extrapolation in these assumptions. The actual numbers are probably somewhere in between.
Is it that China is underreporting new infections for the neighboring provinces now, or that they mis-reported stats of Hubei before?
Anyways, I must say I find it a little disconcerting to see such a statement (which I can only describe as fear-mongering) from the director of the WHO on a public plattform. Does he not have the means to contact officials directly and tell them what they should prepare for? His "call for calm" is 3 tweets in ffs
But as an outside observer just watching the stats, here's my biggest reason for being suspicious regarding the number. Right now there's five other provinces (Guangdong, Zhejiang, Henan, Hunan, and Anhui) with more than 800 confirmed cases.
For context that's the level Hubei (Wuhan) was at three weeks ago. To contextualize when Wuhan had O(1000) cases, before full quarantine, the infection was growing at a rate of 50-100% per day. In contrast all of the aforementioned provinces are now currently keeping growth below the target of 10% per day.
Now obviously, the infection control process will improve over time as we learn more about transmission. But none of those other provinces are in full quarantine like Wuhan. And yet, every single one of them is doing a remarkably better job than Wuhan was at the comparative point in the infection. In fact they're all doing even better than Wuhan did after it locked down to full quarantine.
That kind of rapid improvement in disease transmission control over the span of a few weeks is hard to believe. Every single province seems to be hitting their targets on every single day. Compared to a few weeks ago, the public health improvements are almost too large to be believable. Most likely, I'm being paranoid, but it does smell a little fishy.