I'm not going to say that this was a legitimate attack by any means. Personally, I believe this was just some civilian with hatred towards Japan that attacked the car.
However, I think it's a bit alarming that after recent anti-Japan protests (link to that in additional news links) in China, people start to become
aggressive towards diplomats.
Usually ambassadors are the last to feel the sting of conflicts, since they are the "messengers" between countries in any crisis.
But the fact someone attacked the ambassador car, and ripped off the japanese flag, shows that the whole Asia is lighting up to conflict in recent
If it's just steam blowing off, or a conflict starting to emerge, time will tell.
(visit the link for the full news article)