There's a very short answer for why you're seeing this: You're not looking at your profile page.
To be clear, it could be yours and just be an unregistered account you lost access to, such as by clearing your cookies. If you wrote the answer tied to that account, then it is. But at some point you lost access to that account, logged in with the one you're on now, and now you have a registered account with the same name. (Usernames are not unique on the Stack Exchange network.)
Let's look at your screenshot:
A couple things we can note here tell us we're not looking at your current account.
For starters, check out the "Last seen" date on the right hand side, toward the bottom of the screenshot. The date reads "Jun 25 '12" which can't be right considering you're logged in, right now, on March 4 2016, unless that's not your profile.
There's also no "Edit Profile & Settings" tab- You would see that, since you're logged in, on your own profile.
Finally, check out the top bar. You have 20 less rep than this account, no silver badges, and a profile picture. If you click on your picture up their, you'll be taken to the profile of your current account.
You're likely seeing this profile due to how you're accessing the site. If you have a bookmark, you might have bookmarked the site before you lost access to that account, and just never fixed the bookmark.
You can reclaim your unregistered account by merging it with your current one. You can find instructions on how to do that in the Help Center.