1000BTC is huge for every investor, but compared to the market it is nothing so don't be too skeptical about everything, this is just a normal profit taking action.
Taking profits now with some of your bitcoin is a wise choice, but one may want to sell them now and enjoy them rather than waiting a long time. 1000 bitcoin = $69 million, that's a lot of money to reinvest and diversify into some real assets and also crypto at lower prices.
That guy bought bitcoin for $1 while we bought bitcoin for $10k, $20k, someone even bought it for $40k. That means his profits and ours are very different, even a huge gap. Let's stop imposing our thoughts on others and don't think they are wrong for not waiting a little longer to sell bitcoin at a higher price. If we only spent $1k and made a profit of $60 million, would we want to be more greedy?
Those of us who are buying bitcoin for $20k will sell bitcoin when the price reaches $100k and it only increases 5 times, while his profit is several million times. I don't see any reason to hesitate and not sell them.