Jag is right, the limit is 1100rpm. But in order for them to kick you out for a high idle speed, they have to put their sensor over the engine to take an actual reading.
I get harassed almost every time in my yellow car because the tach reads 200 rpm too high. They see 1200 and threaten to fail me.
Since you checked for exh leaks, it is most likely their sensor wasn't shoved far enough up your pipe. The sensor they use 99% of the time is a solid tube about 2' long. By putting a hose over top of the sensor and your tail pipe, they can help seal out the air that pulses back into the muffler. Did they play with a big black hose? Or, they can break out the flexible sensor and insert it all the way. My guess is that they misplaced their flexible one, lost it, or were too lazy to look for it.