I've been digging into this and here are my thoughts.
1. You've been commenting and participating on the forum for a bit, and disclosing your URL, thus, inviting people to check your site out from Woopra.com. Logical, and actually well done! :D
2. Possibly, a few people searching for information on Woopra, which you've mentioned on your blog and it turns up in the searches, could have jumped from Woopra.com to your site, because they were familiar with it, or who knows. Not sure. Stranger things have happened.
I've been running Woopra for months now, and I searched through all of my referrals and stats for my site and a few of the test sites and can't find Woopra.com anywhere - which ticks me off cause you are getting hits from Woopra and I'm not. NAH! :D
Keep an eye on this and let us know if it pops up again. And thanks! Also, be sure and post this in the bug section in the future so our techs can jump on this stuff immediately.