I believe
  1. No concept of windows
    Like all their buildings are completely solid. They'd come here and ask why our houses have so many holes.
  2. Three biological sexes
    That's right y'all, at least three people have to be involved to make a baby. Not sure how the genitalia would work.
  3. Their version of clapping is what we would call repeatedly farting on command
    And what we would call a bad smell, they would call a pleasant one.
  4. Don't care about history
    They'd be baffled to know how many books we keep about dead people.
  5. Have to eat diamonds to survive
    And then they'd ask us why we put food through little holes in our ears.