In fact he was convicted on the basis of law. The Rules of the Air state:
In this case of particular relevance is S.I. 61 of 2006 The IAA Operations Order; Article 51(3)(b) Only a helicopter operated in Performance Class 1 shall be permitted to operate from elevated heliports in congested areas.
And:
S.I. 216 of 2005 further states:
(d) in the case of a rotorcraft or balloon, not being used for public transport, any place where the aircraft may take-off or land without undue hazard to persons or property and in respect of which the owner or occupier of that place shall have given permission for such use, except that, in the case of a rotorcraft, where that place is of an elevated construction, located on the roof of a building or a structure, it shall also be licensed by the Authority under this Order for such use by that rotorcraft. 5
Taken from the accident investigation report.
Simple as that.
He could still have his license pulled. The IAA has been designated to oversee FAA pilots and aircraft based in Ireland. No doubt a report has been sent to the Feds. This may not be over.