Even a small increase in demand can result in a large price change if it pushes into a different part of the demand curve (e.g., if the "cheap" demand has been supplanted with customers willing to pay more then the market price can change drastically).

It seemed low to me too, but it was the most credible reference I could find. Surely it's an estimate, and I'd guess a conservative one.

Data centers don't buy from stores.

Exactly. Everything worth buying was being snatched and resold before it even saw a store.

A ton of not-data-center-people took mining as a hobby...

And what exactly is the difference between a data centre and a hobbyist running at a similar scale?

The mass of hobby miners NOT running at a datacenter-scale was probably enough to empty stores, which was the point of the original comment.

Miners were only buying high end cards.

Thats not quite true, unless the 3060 Ti counts as a high end card I guess. It was easily the most popular mining card of the 3000 generation, due its excellent MH/Watt compared to the others? And previous to that, the mid-range 5700 from AMD was the best, to the point where you could sell your 5700 to a miner and buy a new 6700 and have cash left over at some points.

I saw the 5700/6700 claim at the time, but I was never able to find someone willing to buy my 5700 for what a good 6700 was selling for.

If nearly all the 60-series cards sold for several months are considered high end cards, what are the low end ones? 710 gt's?