When GS attacked he was not in flight. He transformed to robot mode in front of them he said some words and then attacked. As for which ever group of tanks he attacked, if he was attacking the ones beings attacked by Decepticons he would have dealt with the ones in robot mode first, because as far as he knows there is no such thing as humans, and any vehicle not Autobot is an enemy. As for the method of attack, unless specifically stated he uses everything.

[quote=Pathfinder]
Guardian is a dick. >:C
[/quote]Damn straight.