There are a couple of entries there. One is for active shots, and the other is for "shots that exist in the pools ready to pull out and use."
Basically each visual element needs to take up some space in RAM, to some greater or lesser degree (depends HEAVILY on what it is), and so we need to keep copies of these things and then reuse them. While they are being used, they are out and in one tally, but while they are not in use they are in the pool waiting to be used.
I think that particular one, going from memory, actually shows the difference between the shot objects it had to use (on the left) versus the total number of shots fired since you started this session of this campaign (on the right). So it might have fired 40k shots, but only ever needed to have 2k of them actually exist in RAM, etc.
This gives us some sense of how efficiently parts of RAM are being managed, which also does have some CPU implications.
