I'd say it's probably a coincidence. While Patrick was venerated as a saint in Ireland, with a feast on the anniversary of his death on 17th March, from quite early on, he wasn't recognised in Rome until the 17th century, when he was added to the official church calendar. It's seems unlikely to me that the medieval Irish would've specifically chosen a Roman holiday to co-opt, especially as there's no obvious link between Liberalia and Patrick.

For what it's worth, I seem to have become Askhistorians' resident denier of connections between Christian and pagan Roman festivals. Here are my posts on Valentine's day and Christmas!