The 0.6%+ are probably tourists and I am 100% sure that the entire population of Monaco (although a small one) is not using the internet. I don't know how this is calculated, but it would makes sense if they are distinguishing internet users from local population. It's possible to have more users, than population, simply by including the temporary visitors who use the net. Also, it's possible to have way lower percent of internet users in a place where 100% of the actual residents are using it, just because there are many "ghosts", who are counted as residents but live/are elsewhere and are counted there if they use the net (Monaco).
Anyway, whatever way they are using to calculate the internet population, it's probably not very accurate, but you get the bigger picture.