I didn't believe it either... it seems to be mentioned in a bunch of keto literature online, like this one [1]. Some folks say it stimulates insulin, and some say it upregulates gluconeogenesis. I haven't found anything authoritative, so I remain skeptical.
So, it's just a thing you think might happen, because there is such a thing as gluconeogenesis? I went looking, and the only cite I found was a study suggesting this does not in fact happen.
https://en.wikipedia.org/wiki/Gluconeogenesis