Because even if true neither country wants to go to war, countries test each other's military responses all the time and it never goes much further than sending in jets/ships to watch each other while some diplomatic phone calls take place.
No. You take the losses, put a brave face and spin a story about navigation error. Then if you think you weren't in the wrong and they need to get a lesson you destroy something of theirs a while later.
Btw, I'm not saying that's what's happened. I'm just hypothesizing that in case it happened like that they wouldn't start WW3 over it.