I can't see any part of that article that supports your claim. On the contrary, the article appears to claim that one of the reasons he was resisting so strongly was that handing over the keys would allow full access, though the reporting isn't very clear when it comes to already stored e-mails.

From the article:

' On July 25th, Lavabit petitioned to cancel the subpoena and warrant, arguing that if the “government gains access to Lavabit’s Master Key, it will have unlimited access to not only [the account], but all of the communications and data stored in each of Lavabit’s 400,000 e-mail accounts.” Lavabit also asked the court to unseal its records and permit Levison to speak. '

My source is (was) the lavabit ToS. I was a paying customer of Lavabit and familiar with their ToS.

He made it pretty clear that if you wanted to use his service to hide illegal activity you were SOL.

The TOS seems to be long gone. But wikipedia summarises his stance on legit warrants as opposed to "hand over your SSL private key": http://en.wikipedia.org/wiki/Lavabit