It's a pun. Everybody got quiet at once, prompting Orin to say "An angel passed by." Notice how she and Chen didn't even notice that Tenshi (same reading as angel, but different last kanji) actually passed by.
I didn't know the Japanese also had this saying.
One sure did.She really did just pass by.When You're Talking with Friends and Things Go SilentAn angel just passed by. An idiom literally translated from French, meaning "an awkward silence". And of course, "angel" in Japanese is "Tenshi".ChatterPrattle