I would like more clarification as to what this means. Does this mean the histories are purely client-side? If that's not the case, I don't see how they can make this claim.
Nobody knew it was even available?
As people have pointed out, yes, Apple is a trusted part of the system and could release a new iOS/macOS update that captures these keys but short of that, neither Apple nor law enforcement have any access to your iCloud data.
"iCloud uses a minimum of 128-bit AES encryption and never provides encryption keys to any third parties."
If I interpret this correctly I am first party, Apple is second and third is everyone else.