They just made it up. The heat of Venus has nothing to do with CO2, it has to do with the enormous atmospheric pressure. James Hanson was once on a team studying Venus and that is where he came up with the wrong-headed idea that Venus was once Earth-like.
The only thing earth like about Venus is size. So Venus should be described as earth sized not earth like.
True, today.
This of course tells us nothing at all about whether somewhat earthlike conditions existed at some time in the past, perhaps when the atmosphere wasn't so dense.