As someone who collects handcuffs and does feats of strength, I can tell you, it's not extremely uncommon. I've talked to several officers about this and most have seen it done when drugs are involved.
Mike Dayton used to be an expert on it back in the 70s and would even break name brand cuffs occasionally. Broke his wrist more than once and if you see him now, he still has the scars.
Larger wrists help in this also because of the leverage factor. Most USA made handcuffs approach 1000 pounds before they snap - usually at the swivel. I've heard one source say Peerless snapped at a little over 700 pounds. I saw a video of the hinged S&W cuffs being tested and they took over 1200 pounds to pull them apart.