Is it normal for my boss to insist on two nails for bevel siding?

You were right and your boss was setting that siding up for failure. When you're hanging cedar bevel, the goal is to allow the wood to expand and contract with the seasons. Driving two nails trough the face—expecially if they both hit the stud—effectively pins the board in two spots. Since cedar moves a lot based on humidity, those boards are eventually going to split right down the middle becasue they have nowhere to go when they shrink. Standard practice for bevel siding is a single siding nail per stud, driven just above the lap of the previous course. You want that nail to clear the thin top edge of the board underneath it. This creates a sort of hinge effect where the board is secure but can still 'breathe' behind the lap. If he was worried about cupping, the solution isn't more nails; it's making sure the material is acclimated to the local enviroment before it goes up and ensuring a proper house wrap and rainscreen gap are in place. I've gone back to jobsites where guys used the two-nail method and the results are always ugly. You'll see vertical cracks starting at the nail points within two or three years, especially on the south-facing side of the house where the sun beats on it. It’s a classic case of a contractor prioritizing a 'tight' look on day one over the actual physics of wood.

Since you're looking for a new gig anyway, stick to your guns on the single-nailing technique. Any reputable siding lead or GC who acutally knows thier material specs will see that as a sign you know what you're doing. It’s better to be the guy who does it right than the guy who has to explain to a homeowner why their expensive cedar is splitting three years down the line. If you want to go the extra mile, use stainless steel ring-shank nails so you don't get those nasty black streaks from the tannins reacting with galvanized metal.

Man, sounds like you dodged a bullet. If your boss is throwing hands on camera and forcing you to trash an expensive cedar job, he's a total liability. I've seen guys try that 'two-nail' trick on wider 8-inch bevel thinking they're being smart, but it's just a recipe for a mess.

When you're out looking for the next gig, find a crew that actualy pre-primes all six sides. That's the real pro move for stopping cupping without pinning the wood. Good luck—anything's gotta be better than working for a guy who gets into brawls on a Ring cam.

While the previous points regarding hygroscopic movement are technically sound, it is imperative to also consider the specific gauge and metallurgical composition of your fasteners, as I have observed that even with proper single-nailing, using a smooth-shanked nail in lieu of a ring-shank variety frequently results in significant 'nail pop' when the cedar inevitably cycles thru its seasonal moisture content fluctuations. Furthermore, if you were utilizing the 10-inch or 12-inch nominal widths, the stresses on those single attachment points are immense; I always insist on verifying that the nail penetration into the structural framing is a minimum of one and one-quarter inches to properly counteract the leverage exerted by a warping board.