OK, here’s what a lot of people don’t know about the markets:
There are futures markets that continue trading what are called “index futures” overnight, as well as pre-market and post-market trading on electronic markets.
The 500 point adjustment was the result of the futures markets last night (like when you were going to bed in the US) and the pre-market trading brought the DJIA (and other stocks) into the opening levels you saw when 0930 EST came around and the “normal” market opened.
So to a retail investor looking at the NYSE at 0930 to 0935, it looks like “it moved huge in five minutes” but to the pro’s — the move is over, done, etc — it happened in the prior 12 hours. The antique NYSE is simply catching up to where the markets already are.