I'd do the same if I were him, it's been almost 2 years so why not taking my profit out of it.
Investors like him could have a target price range and volume, possibly he sees it is reaching his target so he sold it at $12k.
9000x12000 is $108,000,000 upon this basic assumption this is a very huge dumping made, would this also create a huge plunge in bitcoin price? any math geek here?
In my point of view, selling half of it would be a better thing to do in order to sustain his investment. There is a chance for the market price to continue increasing. Its price may be stable at this point but possibility is still a possibility, meaning there would always be a chance. I am not asking him to gamble his investment but to simply continue his investment. The amount would still be there, holding the half of it would be giving him a chance to earn more as a reward for his patience from waiting for twenty-two months.
If it's true, then that would be super worth it if s/he bought those on $3k range and sold for todate price. Anyhow seems btc still good at 11kish, so nothing to worry of this dump.
What could be the reason behind his dumping of his coins when he can dump a percentage of what he's holding he could dumped half of it and wait a little more time for Bitcoin to reach $15k this year which is not really remote, I figure that he still has Bitcoin in his other wallets, no investors will want to dump all his coins he is comfortable at selling with that profit.
It might be due to change of interest. He could have moved his Bitcoin investment to other projects which are showing a higher rate of increase of a project that has caught his attention.