To the best of my knowledge, yes. It's possible I once overheard/read it somewhere, and have forgotten the source, but it lingered in my brain somewhere.

In addition, with 100 billion+ people existing throughout the entirety of the human race, it's unlikely I was the first to think of anything I've ever thought.

It's a genuinely great analogy though, and your particular version is excellent. There's a reason similar sayings have echoed through history.

  "Therefore whosoever heareth these sayings of mine, and doeth them,
  I will liken him unto a wise man, which built his house upon a rock:

  And the rain descended, and the floods came, and the winds blew, 
  and beat upon that house; and it fell not: for it was founded upon a rock.

  And every one that heareth these sayings of mine, and doeth them not, 
  shall be likened unto a foolish man, which built his house upon the sand:

  And the rain descended, and the floods came, and the winds blew, 
  and beat upon that house; and it fell: and great was the fall of it."

  Matthew 7:24-27 KJV

(100 billion people) * (the amount of thoughts a person has their life) is quite large, but I think nowhere near the amount of permutations of thoughts and emotions to go with them someone can reasonably have. I bet your thoughts are more unique than you think.

But the thoughts people think aren't evenly distributed -- they primarily center around the same things.

It reminds of the Jimi Hendrix song 'Castles made of sand'. Not exactly the same but definitely some common ground.

https://www.azlyrics.com/lyrics/jimihendrix/castlesmadeofsan...