What happens when you pre-render a PNG sequence in After Effects?

I have a main timeline with smaller compositions on it. I pre-rendered one of the smaller compositions into a PNG sequence and now the smaller composition is updated on the main timeline as... well, a PNG sequence it looks like.

Why did this happen? How can I get it to go back to being a composition? (Using "Revert" and "Undo" are not options...) Thank you!