But it's certainly thoughtless API design. The parameter sounds boolean (am I going to verify the SSL host or not?), and essentially it is, except that not verifying it for some reason takes two forms, and a true value turns out to specify one of them.
Whereas I doubt that the giftedness of the programmer has much to do with their reading the docs. A gifted programmer might assume that the API designer would do the same thing they would, which is to specify this with a boolean argument.
The problem isn't simply that VERIFY_HOST is documented as a scale from 0-2 that people are mistaking for a boolean by not reading the docs. The problem is that the scale is pointless, because the value it is expressing actually is a boolean: you are either verifying SSL certificates properly or you might as well not verify them at all. There is no real scale to express. The whole option actually documents a misunderstanding of SSL/TLS on the part of curl's author.
Also "The most dangerous code in the world" is a bit misleading. I would say the code that runs a Predator drone is a little higher in the danger department.