The [relevant legislation](http://www.irishstatutebook.ie/eli/2020/si/448/made/en/pdf) seems not to have a religious exemption, so they may be right. There's an exemption to travel restrictions for a minister to travel to an empty church from where they can stream a service, but not to hold an in-person service.

Whether you could hold a mass within the rules without a specific exception, I don't know. I suspect you could, if you were careful about it. We may see a renaissance of [mass rocks](https://en.wikipedia.org/wiki/Mass_rock).