Junction Box question for recessed lights

Hi, I've done quite a bit of electrical work around the house before but I have hit on something that makes no sense. I have done the calculations as to how many conductors you can fit into a box for the # of cubic inches. This all makes sense.

Now I am installing remodel-type recessed lights, with the built-in J box. This is a standard 6" remodeling non-IC can that you get from the Orange Box store. It says "Maximum of 8 No 12 conductors (4 in and 4 out)". I don't know what this means. I assumed at first the "8" was the normal conductor count. But that doesn't make a lot of sense. What I *want* to do is:

1. Connect a 12/2 as the supply

2. Connect two 12/2s to branch out to other recessed fixtures

It seems to me that that's no more than 4 in and 4 out. However, it seems to me that total conductor count here would be:

- 2 conductors each 12/2 cable (6 total)

- 2 conductors for the wire that feeds the light itself (2)

- 1 conductor for ground

That totals 9. What's more, the other thing that doesn't make sense is that the box is pretty tiny - I estimate about 12 cu in (3.5 x 2.5 x 1.5, more or less). How could you fit 8 12/2s in 12 cu in - wouldn't that require 18 cu in?