It wasn't a communication cable, it was an underwater antenna. The sub was probably atepting to do some maintenance on it, or it may have simply happened upon it by accident. Who knows?
One thig I'm pretty sure of is that they weren't trying to tamper with transatlantic cable traffic with a submarine in the northwester Pacific Ocean some 9000 miles from the nearest transatlantic cable. That would have been a feat well beyond the capability of the Russians even if they had the intention..
Yes, the nature of the entanglement was sorted out quite a few posts ago, and yes, I noticed the "transatlantic" off east asia thing moments after posting but figured freepers knew what I meant, and not get nitpicky about it. Guess I figured wrong.