Essentially true is very different from a lie.
If a dealer advertises that he has a thousand cars and only has 980, that is essentially true. The difference between the literal truth and 1,000 does not matter to the vast majority of customers. If he has 200 cars, that is pretty much a Bill Clinton lie with only the vaguest connection to the truth. If he has no cars at all, just rust stains, that is an Obama lie. Carson’s comments were, so far as I have seen, close enough to true for the purpose for which he wrote his biography.
If a woman on a dating site describes herself as 5’2 and 130 pounds, and she is actually 5’ 1.5” and 134 pounds, that is essentially true and she will look like she is expected to look. The height rounds to her claim, and the weight would be accurate at the end of a long workout without any water. If she is actually 170 pounds, that is a Clinton lie, and the interaction will be significantly different than expected. If she is a 350 pound man, that is an Obama lie. There is a huge difference between close enough to true that it doesn’t matter and so far from true that it sounds like Hillary landing in Bosnia and dodging sniper fire.
The last couple years that I consulted, I charged liberals 2-3 times what I charged conservative candidates. If they objected, I told them that was my rate and they were welcome to go elsewhere if they thought my services were not worth the price. My claim was essentially true, Those were not my rates for decent people, but they were my rates for people I despised.
“Essentially true” = not actually true