The approach would even under FAA rules be illegal, it's a congested area with absolutely now where to go in case of an emergency. If you fly N-Reg in Ireland (or in any other country) you have to apply with IAA and FAA rules, obviously IAA rules come first.
Second of all the guy was flying without a license! A student pilot certificate is not a license. The current FAA database lists this man as a student pilot, and the FAA database doesn't lie. It takes about 3 months after the exam before the results show, but if a license is issued it always shows up in the database.
But what can the IAA or Gardai do in cases where somebody decides to fly a helicopter/airplane without a license?? How will they stop it?