Do note that Facebook automatically groups 'close friends' based on your interaction with them. It's worth double-checking to see if anybody is in your 'close friends' (and other) groups because while you may not have explicitly done so, Facebook may have done it for you.

Good tip. I checked it but "close friends" is empty.

But you may be right. Even though i don't interact on Facebook; i only check what videos/pics/news they shared and click the ones that i am interested in. (not even 'like' them)

But as you said, Facebook is probably tracking my 'clicked news/pics' and show those friends' activities.

I will monitor it for some time.

Thank you all for the tips. Have a great weekend.