I would say that "fake Irish" would be the names that Americans and Australians think are Irish but did not originate in
Ireland, such as
Colleen and
Megan.
Of course, during the last 30 years the Irish themselves have been affected by the same desire to find uncommon names for their kids that has spread across the entire "developed" world. So there evidently now are a few girls born in
Ireland named
Colleen, though I don't think any of them would be over about 25 years old.
The love of "Irish" names isn't something very new -- in the USA I think this is actually the oldest "ethnic name" fashion. The average American
Colleen is now someplace between 40 and 60 years old, after all.