expensive tastes in weaponry
Yep, and I'll bet I know why he chose it. That model is SIG's take on the "updated" AR with piston-type gas system. Like a few other similar rifles, the action spring has been moved up front, under the hand guard. No more moving buffer and spring inside the buttstock, so they could put a side-folding buttstock on it.
In short, it's an AR variant - but one that's more concealable than most.