They didn't bring up the whole 'was the asteroid really re-directed' thing of the movie. Based on their society, I wouldn't put it passed them to use a random Asteroid hit and use it to propagate their propaganda machine.
Yep. For those who who aren't aware (is there anyone? Besides maybe Mike and Jay?), it's not made explicitly clear in the movie, but the humans stepped on the bugs turf, and then the bugs and humans went to war (as Mike explained). But the major motivator on the human side of the war is that the bugs pushed a rock from their side of space, and they deliberately dropped it on the populated city of Buenos Aries.
But that's an astronomically long shot, and bugs don't appear to have the technology to push a rock at FTL speeds, and the rock hit Earth at much lower speeds (an FTL rock would have destroyed the Earth), while Earth clearly has the technology to detect and prevent such an attack.
Buenos Aries was a false flag attack. The bugs had nothing to do with it. The human government destroyed one of their own cities in order to rally and motivate humanity to fight and conquer a race that the human government had just gone to war with.