Not really. There are plenty of low-profile high-net-worth miners with that much. I used to hang out in the cex.io chatroom back in 2014 and there were fat cat miners in there who would say "watch this" and then the price would quickly go down by several percentage points because their entire mining pool just sold. It seems quite plausible at least to me that one of these networks might decide to donate a large amount all at once.
This is really cool to read, but trading volume of btc went from 20M when it was 3 years old to 170M over the years, so that happens a lot less frequently.
These days, many of these same individuals are literally buying plane-loads of chips fresh off the assembly lines in China, and have significantly scaled up their operations with their previous gains, so I wouldn't count it out.
