His previous sales were much lower, per-piece:

"Mike Winkelmann never used to call himself an artist. But that was before he made $3.5 million in a single weekend from selling his artworks. In December, he auctioned off multiple editions of three digital artworks, each priced at $969, and 21 unique works, most of which sold for about $100,000 each. It was only the second time he had put his art on sale."

https://www.nytimes.com/2021/02/24/arts/design/christies-bee...

So from $100k/piece up to $6.6M.