Referring to past times with "hence"

From Tor.com, an interesting use of the word hence:

Minutes ago, J.K. Rowling finally announced her plans behind Pottermore, the mysterious website that appeared a week hence with only a “Coming Soon” sign to warns readers and fans.

For me, the word hence can only be used to refer to times in the future, and the writer of the above quote should have used ago. However, hence is a pretty rare word, and it's possible that the past usage of hence is in fact standard, but I've never noticed it.

Is the past usage of hence sanctioned by any important authorities? Does it have a long tradition of usage? Or did the writer trip herself up trying to be fancy?

Update: The answers below all agree, but I'm looking for someone that can produce some actual evidence from usage or a respected authority. I've started a bounty with that in mind.

Solution 1:

Evidence from dictionaries:

Hence, when applied to time, is defined as:

2. from this time; from now: They will leave a month hence.

There is not a shred of evidence in any dictionary or in common/traditional/standard usage that hence can be used to refer to the past. So, as it is unsanctioned by any important authorities, and unused, I would say this is a case of either misconception or mistake on the writer's part.

In the quote, ago is the proper word to replace hence with. It is possible that the writer confused hence with since, as since is sometimes used as a synonym of ago.

Solution 2:

The definition and etymology show hence is meant to be a "future time"

I think it could be a typo for thence

from that time; thenceforth