Ok, I see a bunch of bad takes in here, and it's really the fault of the article for not explaining what is going on.

It's actually kinda simple. The researchers just give the AI a chance to replay previous memories without interference from new data. As this is similar to what our brains do during sleep, the comparison is obvious. The researchers themselves use the words "sleep" and "replay", for context.

They explain this in some detail starting on page 7 of the original paper. The results do seem to indicate that just letting the AI replay its memories was enough to protect the original learned behavior.

I'm looking forward to going through the math later; they seem to provide quite a bit.

One final thought: I'm surprised that vice didn't use the idea that the AI was dreaming; it seems like that would have been an obvious idea that would have made the headline pop even more.