Yes, that’s mostly correct – you pay for the theme, and then you have a “download” area where you can click a link to download the theme in a .zip file.
But, licenses don’t keep people from “repurposing” your code. Mostly, this seems to be an acceptable practice as I’ve seen several themes with the same code in them. The community pretty much polices themselves and vigorously defends designs, though. If someone rips off a theme, Envato will usually take the offending theme down. Or if it’s selling on another theme site, usually those companies will take the offending themes down, too. Or, you can do DMCA takedown notices for copyright violations.
I don’t work for Envato, and I’m not an authority on the subject. These are just my own understandings from observations over the years. I could be wrong.
Don’t let any of this discourage you, though. There is risk in everything. But, there are also several authors making very nice livings selling themes on ThemeForest. And it’s a great community of people who are all very supportive. Nothing great comes without risk.
Hope that helps!