i think presently it is not the global currency of the earth becasue so many people do not know any thing about it. but it is look like that in future it may be the global currency of the world.
Very few people across the globe are aware about the bitcoin and that doesn't make it global currency, but things may change in future when it will be widely used and accepted.
If people say that bitcoin is a global currency now, I think they are saying wrong. Many countries in the world are not known about this currency. If a a country using bitcoin, than only a few people of it are using bitcoin. If this currency is to become global, then it should be spread out widely. More they known about it, more they become interested in it. Only internet is not only a source of awareness about bitcoins, I think it should be started at higher level.
You are right about the thing that we cannot claim bitcoin a global currency as it is not used globally. But it is used online globally and there is no restrictions of boundaries.