He was on a trajectory to success. Doesn't his left4k dead game just about predate Minecraft and that gained some traction in press and got a lot of plays. This probably help build his profile and gather more followers on twitter. This in turn would have helped minecraft get an initial uptick. Obviously helped by it being a fun game with potential if you are into that type of game.
So yep luck that his success was so big but he probably would have had some success at some point.