First of all, if you ever participate in iTunes' free singles, those will obviously count as iTunes tracks. (It used to be called Single of the Week, I believe, but now it's found just under "Free on iTunes" on the Mac/PC versions of iTunes.)
By the same token, participating in any of those promotions - 12 Days of Christmas, iTunes Festival, etc. where music can be "purchased for free", those will count as tracks in your iTunes library that you can retrieve via iCloud.
Also, some tracks over the years came with free bonus downloads. You'd buy one song and some other promo song would be attached. Through the years, iTunes has done all sorts of weird, interesting and sometimes confusing promotions. (Among others, there was a Starbucks free song promo, the Pepsi 100 million free songs promo, etc.etc.)
The final obvious option is someone gifted the song to you at some point, for some reason.
If you want to figure out exactly what happened, you can check your purchase history in iTunes. On a computer, go to the iTunes store in iTunes, then at the top of the store UI, click your user account Email address and then choose Account. Provide your Apple ID password, then scroll down to Purchase History and click "Show All". If you have a long history with iTunes (I got in the game in 2003 when it all started!!!) then it may take a bit of time. Look through the list and find out if these tracks are appearing in any purchase. I'm not sure if received gifts show up in purchase history, but anything you actively clicked on "buy" or "download" will show up - even free stuff.
(I don't know your situation, but perhaps someone accidentally purchased it using your device? And the 99 cent charge would be easy to miss if you're not a person who carefully monitors your credit card bills...)
If you seriously do not see the tracks anywhere in your account, but they are still showing up as iCloud tracks in iTunes, then it could simply be an Apple glitch. Weirder things have been known to happen. If you buy a lot of music, you can't really "disable" just those two songs, but you can remove them from any playlists, and you can uncheck them in iTunes on your computer.
Hope this helps.