Hmm, not sure if this helps, or just muddies it even more, but they were discussing it hereAlso we do not know if the 2880 SCU of cargo is including the shops or not. The Privateer has 2658 SCU total if we include the 8 public and 2 private shops.
There was some ambiguity to that dialogue, but the way I see it, they're comparing the number "around 2800" to what the Hull C can carry, and basically talking as if that 2800 is cargo not including shop inventories.
Additionally, based on the cargo hold size, that space seems more than adequate to hold 3000ish cargo. Here is how I got there: the side view shows 5*3*3 of those really long containers. In the picture of the crane operator, we see there are two of those 5*3*3 container stacks with a path in the middle. Those containers are four times (Well, 4.35 times to be exact but it's a concept image and I'm not sure which pixel is the actual corner) as long as they are tall, so they should be something like 8*2*2 SCU containers. Coincidentally, or perhaps not so coincidentally, 8*2*2 * 5*3*3 * 2 gives you 2880 SCU capacity for the cargo hold.
I'd really turn this issue around, and say we don't know if the shops bring in additional inventory space, or if they just sell directly from the cargo hold. But I'm reasonably certain that, at least at this time, 2880 refers to the cargo hold capacity.