I have noticed this a couple of times, where I am scrolling through my News Feed and come across a post (spam, typically) from a page that does not look familiar to me. Today it was a page called "Rock Music Community."
I tapped the name and was taken to the page itself, where it showed that I had liked and followed it. This is odd considering the two facts below, which I know to be true:
1) I use a secure password and keep track of active Facebook sessions. I am certain no one else is using my account in a malicious way.
2) I know for a fact that I never went to a page named "Rock Music Community" and pressed the like button.
That said, what is the deal? It has happened 4-5 times in the past as well, with different pages. Has anyone else experienced this?
Many years ago, when FB went through one of their conversions of "old data" to "new data" -- your old FB profile's data was probably converted. For example if you had a FB account from its college days say in 2005, and in the "hobbies/interests" section you put "Rock music", at one point when FB converted those fields into FB page likes for you automatically, it tried to search for the closest match to "Rock music" and ended up on some random "Rock Music Community" page. I know this was the case for me for a few things and I went and unliked them manually.
Check out https://www.facebook.com/[yourfbname]/likes and see if you find more similar pages being liked by you.