There's one thing I read differently from your description above. I don't think they're saying the GRB (if indeed it was one) was not observed because no gamma ray telescope was pointed in its direction. I think they're saying it wasn't observed because the gamma rays are emitted in a tight beam that didn't happen to be aimed at the pale blue dot.

The most interesting implication is that the source of the burst emits its optical afterglow in a less tightly beamed manner than the actual burst. Thus we may be able to see a lot more of these events if we look for the optical afterglow rather than the gamma rays themselves.

One question comes to mind: are the GRB's that we do observe actually occuring in the time frame we see them, or are we just seeing the beam sweep by, and the burst itself is longer-lasting? (They still must be fairly short-duration, or we would see two or more pulses sometimes as the object rotated "our way" again.)