Did Dragon cause the lightning at Lougetown I watched the anime at least twice but I don't understand. I know Dragon saved Luffy from Smoker but did he save Luffy at the execution stand? Bartholomew said he was stunned when he saw the lightning save Luffy. That makes me think it was Luffy's unexplainable luck, like when Fujitora rolled the dice to pursue Luffy
To answer cannonically, no he did not. As far as we know Dragon was not involved in that scenario and the reason why he survived is because of his incredibly high luck. 

To answer speculatingly, There is some suspicion that this luck stems from the fact that he carries the "Will of D" whereas he must be an integral person to change the world. 

The truth is however, given that he series is still in production (and probably will be for some time). We do not have enough data to say true or false. We can only form opinions off of what we do know.