You assume that it didn't happen because you didn't see it? If there's a conspiracy to commit violence that culminates in the throwing of a Molotov cocktail, I'd certainly consider the act of throwing it an overt act to further that conspiracy.
I want those charged to have a fair defense (which is unfortunately not a given in the US), but I also don't have a problem with these charges in general. To call the charges ridiculous seems biased at best.