There is a good chance it could be anything, given the generic tag, and most of those tags are not labeled right anyway at some stores. I would plant it where you want it and see what it does. Many hostas grow a little slow so it could take several years to get that large. Many only reach those large sizes under ideal conditions. You can always divide it out and not allow it to get that large. This is not a shrub like plant that will have invasive roots and take over.
