But then how do you explain the 10 round pistol mags?

Don't they fall into that category?
Well, kind of. I think the CX4 carbine kind of pushed this issue first because there suddenly was a semi auto rifle that could accept currently existing legal 10 round pistol mags. They read the law and realized that it's the mag itself that is legal or not, not what the mag happens to be in.
CFC basically decided that they could live with 10 round mags in a semi auto rifle is the bottom line. I personally think that the law allows unlimited AR15 style magazines at this point due to the 7615, but CFC feels differently.
The 10 round A1A enfield mags were approved for import, and they happen to work in M14's... and that has nothing to do with the 10 round capacity. 30 round A1A Enfield mags would be legal too, and still legal when put in a M14.
I think they let the cat out of the bag when they said outright that the LAR-10 pistol mags are legal. If 5 round AR15 semi auto rifle mags are legal, and 10 round AR15 pistol mags are legal, then 30/40/100 round 7615 mags should be legal, whether the 7615 was advertised with the capability to use AR15 mags or not. The AR15 pistols were obviously designed to use AR15 format magazines... so shouldn't they have been limited to 5? the AR15 pistols were designed to use AR15 mags, and they decided that 10 round mags were ok because they were a pistol. The 7615 was designed to use AR15 mags, and it's limited to 5?
I guess the choice is: Design a bolt action rifle that uses a mag that does NOT fit a AR15 without modifying the magwell and hope that CFC follows the letter of the law, OR, get charged for posessing a 30 round AR15 mag and argue that it is a 7615 mag, which just happens to fit in an AR15, and use the LAR15 mag ruling as evidence to support your position, along with the CX4 and M14 mags out there as additional evidence.