Q: Angry Birds update, but not owned?

The search for " _MASReceipt" did the trick. However, I used the app EasyFind, it's FREE! A quick suggestion if you dl'd Final Cut you more likely dl'd Motion as well, which was the app I needed to delete to get rid of Angry Birds. The indicator for me was the "date". Hope this helps you as it helped me after 2 years of Angry Birds being on my comp. I am finally FREE!  The H-E- double hockey sticks to Angry Birds. 

Thank you Dah.veed! You rock! perfect solution to the problem!

Thanks Mate,  you're a legend, I have exactly the same problem and your solution fixed it. Thanks for sharing!

You're a hero! I've had this problem annoying me for so long and now it's finally gone.

Thanks!!

Thanks @Dahveed for the solution!

Without addressing my opinion on the piracy issue and the Angry Birds update being a result of that, let me share what I've found:

All 3 of my Macs are logged in with the same Apple ID. I migrated 2010(?)MBP to 2011iMac to most recent MBP, which I purchased in late September.
3rd-party software that isn't freeware/shareware (from legit & reliable sources) has been purchased/downloaded from the App Store. I try to use the store for all software because it's easier to keep the continuity of the contents of my devices. My older MBP is running the most recent Yosemite Dev preview. My iMac is using 10.9.5, as is my newer MBP.

The only piece of software that is from a different source or unique is one that I downloaded from the App Store only onto my newer MBP. It's called "Astro" and is a Facebook Messenger app for Mac. I tend to clean, uninstall, install, update all three of my Macs at the same time, solely for my preference of preserving continuity. The App store doesn't show an invalid update to Angry Birds on anything but my newer MBP, which again is only different from my other Macs by having this Astro app. It's the glitchiest app I've ever downloaded, doesn't sync with Facebook and has an update every couple of days. I first noticed this Angry Birds issue after installing Astro.

I'm fairly certain all my apps are legitimate and I've searched all 16 _MASReceipt's in the package contents of my apps. I can't find a single anomaly.
The only caveat is, I changed my Apple ID shortly before installing this piece of software. It is the only piece of software I've purchased or installed since changing the ID. Updates with this new Apple ID seem fine on all 3 Macs and my iPhone & iPad.

While I don't question your answer for why Angry Birds could appear erroneously in someone's app update list, is this the only reason you know of?

Thanks for any insight you can provide!

The anomaly would be that you have 16 _MASReceipts and only 15 apps listed in the complete (no hidden apps) Purchases list in the Mac App Store. The app with a _MASReceipt not in the list is the culprit. Of course you complicate the issue if you now are populating your Macs with apps bought with two different Apple IDs. You need to compile a combined list from both Apple IDs Purchases lists to compare with the total apps with the receipt installed on your Mac. (It is generally a bad idea to create more than one Apple ID.)

It has been reported that there are some 3rd party developers who are not distributing their apps through the MAS, but have been placing legitimate MAS receipts from other developer's MAS apps into their app's bundle to get the app seen by Spotlight. I forget what this was supposed to accomplish for them.

Thank you!  This has been driving me crazy for a while.  I had four apps that had these receipts so I just deleted all of them.  Seemed to do the trick. 

Thank you it worked!  I bought my mac used and thought I had removed all of the pirated software. Just found out that the Angry Birds update was really a program called Motion.  With you help I got it off my computer and the Angry Birds update is gone.  Thanks you!!!