Well I gather we should really call them the IAA...
Simple, really. There aren't a lot of 146/RJ drivers around in the first place, and even fewer who are current within the last 3-6 months, which is what Cityjet have required for at least the last year or so. Cityjet clearly believe that non-current 146/RJ pilots pose a training risk, so they would rather have nice, current Americans. Once that resource dries up, they may well start taking the un-current guys, in fact they will probably end up training a whole bunch from scratch. There simply aren't that many rated people around any more, most have long since moved to the 737 or A320 or are quite happy to stay where they are, and get trained on new equipment as more 146s are retired.
like to know within Cityjet would make that exact statement
It didn't come from Cityjet, it came from (more than one) agency. However it is obvious that Cityjet/Sigmar have made an approach to the government to get this done, and I would imagine an exception was made as a result of a really dark picture being drawn by Cityjet. They are going to have problems crewing all those aircraft, irrespective of where the crews come from.
Most Equal Opportunity legislation allows for the case where a company can show that there are no suitably qualified locals who can do the job. In this case, it would be relatively easy to demonstrate that there weren't sufficient qualified and current pilots in IRELAND to fill the seats, but I doubt they would have to make their case for the whole of Europe.
The alternative would be to invest in a little extra training for those who are rated but not current, and who are EU citizens. The upside is that they are not as likely to get sick of CDG or DUB and want to go home.