It could be that the sudden purge of air to raise the tag is enough to signal the air compressor to start...mine does the same occasionally.
BTW, I'm the second owner of a 2008 Contessa. I believe the air compressor sensor switch was plumbed incorrectly from the factory. It cycled on and off far too often. As it turned out, the pressure sensor switch was connected to the air compressor through a T. The line going to the compressor from the storage tank has a check valve at the tank to prevent air escaping from the tank through the compressor pump. The check valve is required and installed where it should have been. All air compressors will eventually leak down. I moved the sensor to another fitting on the storage tank and the compressor seldom ever comes on. I'll be out for over a week this coming week, so I can tell just how often it runs during extended use. Right now, it hasn't cycled once in over 24 hours that I heard.
Gil