Tires Plus in Morrisville PA did a similar thing to me a couple years ago.

TP: "Your brakes failed inspection"

Me: "What was the measurement on your dial caliper?"

TP: "I will have to review that"

Me:"Keep the brakes on, I'm coming to get my car so I can measure and replace the brakes at home, I'll pay another inspection fee"

Me: (Drives to Tires Plus)

TP: "Oh, your car passed inspection, turns out there was enough on there to pass"

I still had 5/16 left. Plenty of meat to use before the whine, brake work is service center's bread-and-butter and the incentive for them to rip you off is very high.