Disclaimer: I am a Greek citizen.
Feel free to take cameras with you and take pictures of the beautiful scenery, monuments and people. When however, you go outside military facilities that have big "NO PHOTOGRAPHY ALLOWED" signs (in english and actual no camera icons in case you don't know english) and start taking detailed photographs with your DSLR and 70-300 lens, expect to be arrested if caught. The devs should absolutely have requested a license to do it, they didn't care to do it or got caught in the bureaucracy that is to be expected with these affairs, they got arrested for breaking the law. If they were caught doing that in the US (say, outside Nellis AFB), I wonder what would have happened to them.