[T]he whole sequence of events as presented in the movie is scientifically nonsensical, and Countdown's version adds even more impossibilities and absurdities to the account. (For instance, asserting that Hobus was one of the oldest stars in the galaxy. Stars that old don't go supernova. It's something that only happens to very large, very short-lived stars.) So I'd hesitate to accept anything we've been told about the supernova, canonically or otherwise, at face value. It happened, but the rest is subject to interpretation.
It's easiest for me to believe that someone broke Hobus. None of the other supernova described in Trek
produced FTL shockwaves of this sort, and even when others agreed with Spock's analysis it seems like they underestimated the shockwave's speed. The second Countdown comic
suggests that the experts expected the shockwave to arrive in weeks, not in the shorter time that Countdown
may have implied. Someone--or something--may have been experimenting ...