Most of the cases I've encountered are white SJWs looking for any reason to seem more special and oppressed than they really are, and fixating on their Irish/Celtic heritage. Naturally, they also tend to be into paganism/Wicca/witchcraft and other such woo-woo nonsense. Knew a married couple online who were exactly like that - woke Californian hippies, converted to some neo-pagan religion, changed their boring normie names to fanciful sounding Celtic ones, had three kids with equally ridiculous Irish/Welsh names (until the eldest trooned out and gave himself a typical tranny name).
Unfortunately, plastic paddies of that kind are common in Australia as well and I've met a few - majority of white Aussies probably have an Irish convict in their family tree somewhere, and a lot of the surnames have stuck around so you'll meet plenty of Sullivans and McSomethings, but it gets ridiculous when they start believing in fairies despite their most recent Oirish ancestors likely being very, very Catholic.