Nuclear submarines, and especially ballistic missile submarines, don't communicate with anyone at sea unless it's absolutely critical. Communicating gives away your position, and for such submarines, the fact that nobody outside the hull knows exactly where it is is their number one means of survivability. In addition, ballistic missile subs don't have 'allies' - they treat even the surface and submarine forces of their own navy as 'potential hostiles' when at sea in order to maximize their survivability and to continually train to avoid such threats.
Collisions between submarines were fairly common during the Cold War, and were indicative of the amount of time subs spent playing 'hide and seek' with their opponents - because in order to gain intelligence on other submarines, or even to follow them reliably, subs have to be quite close relative to how long it takes them to stop or turn. As a result, however, most collisions were between or involved attack submarines. For two SSBNs to involved in such a bump, either one or the other had to be involved in SSN-like games, or pretty astronomical odds were just surmounted in a random collision. It's a big ocean. It'll be interesting to see precisely where the damage to the two boats is, as it might tell us what aspect they collided at - I have heard it was a slight angle from head-on. Even that doesn't meant they weren't playing silly buggers - if one submarine turned to check its baffles and the other didn't maneuver out of the way, that could result in an angled head-on.