Old school lifters used to do pullovers to expand their ribcage - there's no evidence either way on this but IMO it probably doesn't unless your in your early 20's...and even then its only a maybe.
Bbell/dumbbell pullovers happen to suck for chest & lat development, which is why smart bodybuilders gave up on the move (unless they had access to a pullover machine). Ribcage expansion isn't as important as chest/back growth.zx
So yes, its broscience