Having gone to the article hoping for details on why Dyson disbelieves global warming, I'm disappointed like you. On reflection, I think the author intended the article to be about Dyson himself, and as such, I kind of like the writing. But, yeah, I'm disappointed about the lack of details.
The title of the article here is misleading. He isn't the global warming heretic, he's always been a heretic in everything that he's done or talked about. The simple fact is he's quite often accurate.
The article is more of a character study and description of modern science when it crosses into politics / pop-culture.
Dyson's view is simple: he thinks the doom & gloom predictions of those who are forecasting the end of life within the next hundred years is simply not borne out by the facts.
This is important because Dyson's opponents as a rule try some sort of character assassination instead of sticking to the subject matter.