I am curious if it's a coincidence or if it's really the transaction that sold those Bitcoin on the market immediately.
I have a feeling that some of those coins are owned by people who have left their wallets forgotten on various HDDs and the latest ATH made them look for their old money, look for programs to recover old deleted files and so on. And since that takes time, some of those moves happen this late.
I mean that it may be also a relation between these findings and the increase of topics made by people asking how to get their hands on their old wallets...
Of course, it may not cover all that money.
Also I expect people only sell small parts of those riches, but it still counts as big amounts of dormant money being moved, since the entire inputs are spent; plus the change may go to new, SegWit addresses too.
Or only people triggered the dumps because they saw some transactions transferring Bitcoins from Bitcoin addresses with no activity from 7-9 years.
In the days of bearish market people can get scared by anything and everything can be exploited by smart bears. I don't think though that the current price is that much related to those old funds on the move.