It's not really about the RTL-SDR. The person who was arrested was using the device to probe stuff that the Tunisian government doesn't want to be made known.

It's not really about the RTL-SDR. The person who was arrested was using the device to probe stuff that the Tunisian government doesn't want to be made known. If he had been using binoculars and a notebook at the airport, he would have been arrested too. They were watching him, knew what he was doing there, and used whatever pretext was at hand to arrest him upon arrival (which suggests he had been there before).