[Caged Great]

See, Littlefinger and Varys both used little birds to observe the goings on in the realm and strategize based off the whispers from the birds.

Bran also uses birds, and likely other animals to do his observations of the past, especially where there are no weirwoods. In the Chaos is a ladder speech by LF, a bird can be heard in the background during the scene. Bran could be warging through time using any animal as a spy in order to know everything. That could also be why he might not know certain things like LF betraying Ned for example, while knowing other things.