In the '70's and '80's, during the cold war, NATO and Warsaw pact vessels' used to manuever very agressively around each other, in international waters. Agressively enough that there were a few collisions. Possibly, Standing orders are NOT to fire on any vessel, unless it's designated or proven to be hostile, or by direct order of the president, or congress.
To me, this seemed more of a political/diplomatic move.