Does anybody know if this is even notionally accurate? Did Venus really go through a phase of temperatures where earthtype life could have developed? Or did they just make this up?
Probably mostly made up. Last I heard there were several, maybe as many as half a dozen different theories on how the planets and solar system formed. All of them very workable, very believable. None can be resoundingly proven nor dis-proven. That's for something as fundamental as how the planets formed.
As to what stages surface conditions might have gone through we just barely (I think) agree on what probably happened here. Note, we are here with all kinds of access to the planet. IIRC there are a number of viable theories on Mars' history. None particularly outstanding over the others as more likely or not. Now, we know a heck of a lot more about Mars than we do Venus. Any theories on what stages Venus may have gone through are based on even thinner evidence than we have for Mars.
So I'm sure (no, I haven't bothered to check) there are probably a dozen or so theories on Venus' history. Sure, at least one of them probably has some fanciful "hey it was once livable" component to it. So the producers could latch onto that and put it forward as "scientific theory" and give it an air of legitimacy.
I'll take "make this up" for $500, Sherman.
For an interesting take on Venus, see "Worlds in Collision" by Immanuel Velikovsky, 1950.
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.
You ask too many questions; you must be a denier.
Intellectually dishonest program when they don’t tell the whole truth. The fact is that Venus has no magnetic field and was blasted by solar radiation. If the Earth lost its magnetic field, it would cause the oceans to boil off and look a lot like Venus.