Hi. Is the bold ていた used here because the action 溢れる happened before the action 折紙が現れる? And the state of being open-air continued until 折紙が現れる?
If so, can we use 溢れている here? Because, according to the context, the the wall of the classroom has been destroyed so the classroom is still being open-air at the time when 折紙 appears and the open-airness is going to continue.
And can I think, compared with 溢れている, 溢れていた is focusing more on the period prior to the appearance of 折紙? And 溢れている is focusing more on the period at or after the time when 折紙 appears? Thank you.