He's referencing that we have early 20th and late 19th century case law about third parties holding documents, etc, that is used to make everything sitting at a cloud service subject to subpoena without a warrant (email, etc, too).
There's all kinds of precedent that was based on sane tradeoffs for the 1800's that doesn't make sense anymore with the more complicated ways we transact and interact and with the ability of technology to commit mass surveillance.