Not sure why there’s need to be a discussion about whose idea it was, since it’s a community project and anyone can and should work towards a single goal: Creating a entertaining, funny and awesome game.
That aside, the idea of nested inventories was fist posted to github by jjs2 at the 16. of October 2013. It was later stated by Kevin Grenade that… This is something we've planned for a loooong time., indicating that the idea is even older than that.