I'm not convinced it's a photon torpedo. I think it might be the Starfleet equivalent of an unmanned drone, particularly since what we saw from the KRE-O Toys that included an Enterprise with 'fighter pods'. It looks like it has a separate set of engines in the back, which you wouldn't expect if it was just a torpedo or probe.
The KRE-O toys included a volcano playset, and a Klingon Bird of Prey, both of which we know appear in the movie. So it stands to reason that the so called 'fighter pods' will appear as well. This may very well be them.
I've been leaning toward it being the Starfleet version of a predator drone.