It's a voluntary poll, hence not reliable. I would never trust an HN poll for something as significant as this. If the results were true it would be worrying, but we need much stronger evidence than this.
So either 2% of all HN readers have had their AdSense account banned, or the poll results are a bit noisy :)
(Obviously this is extremely rough math, but allowing for a huge error margin, 0.5% of HN readers would still seem too high, at least to me)
On saying that, AdSense is an enormous program
Actually, HN has grown exponentially since 2011. You'll have to extrapolate this chart: https://news.ycombinator.com/item?id=5253773
Also, the traffic fluctuates depending on which part of the day you measure. There are comparatively few people here during 3AM - 7AM in the US.