Sinn Féin are not exactly ideological soulmates to many Eurosceptics in the UK. So I can well imagine that many are looking on in amazement at which side they've found themselves on. Of course to attribute this result to Sinn Féin alone would be absurd - they're only a tiny force in the Dáil and it seems that other campaigners and general scepticism have contributed as much to this result.
Now the big question is whether or not this "No" vote will be accepted by an EU that is notoriously weak when it comes to democracy. Or will the Irish have to have more referendums until they "get it right"?