If they sold, people bought it for cheaper. I would understand if the idea of market cap was true and there was a magical pot that holds a ton of money that devs pull from, but I remember someone telling me when I first started that market cap was a joke, and there is no magic pot—it's all peer-to-peer transactions. So the question is not how much money they made from selling it, because they did not make millions. They made far less, because, as you said, someone bought it for cheaper—likely because people had orders (not getting into margins) for lower prices set up. And they rode that into the ground, taking everything they could along the way.
"Oh, this spot price is $1.00—I'm going to set up a buy at $0.50 because this looks like it has a good Wyckoff squiggle pattern and solid double golden cross formations" (that the people who rugged it set up on purpose over months). And when the iron is hot and the order books show a nice enough amount that they can drain from everyone, they sell off all at once before anyone (your AI bot overlords included) can even make a move.
Did they get the amount that the market cap was before it tanked? Absolutely not—but that isn't even the point. The devs knew these people were manipulating the market, and they knew it was about to go down, so they themselves took funds and got into a position to capitalize on the downfall of all the people they convinced that this thing was as valuable as the market cap showed.
And at the end of the day, this is all because none of this is an investment like a stock. When you trade currency on a market, the devs or the people marketing the token do not get any benefit from that. They themselves need to sell the asset in order to make a profit. And that's what you have here—devs seeing the impending collapse because they knew these people were manipulating the market all along, and decided to join in and cover their own ass before anyone else knew what was going on.