Version numbers and alpha/beta/delta labels vary and are subjective in practice. I've seen plenty of examples and counter-examples of version numbers and beta labels to not put much merit toward such labels.
Yes, it is unfinished. I'd rather have Apple do what it's doing -- i.e., releasing Swift as a beta and changing things with feedback -- than do the opposite, which would be keeping it closed until it was super polished as they felt it internally.
I hate seeing this "damned if you do, damned if you don't" scenario all the time.
(1) Pre-release for feedback, get complained at for it not being finished.
(2) Polish and release later on, get complained at for not opening it up earlier for public feedback and testing.
Apple has clearly stated that it's pre-release, that it's not set in stone yet, and that they're open to feedback (which they have been).