The government already mostly uses accounting instead of physical money so moving to a really expensive way of doing accounting probably wouldn't save money.
I think they were trying to intimate that a large-scale adopted cryptocurrency could replace large swaths of financial infrastructure (this is a sort of pie-in-the-sky ideal, but something like it could happen) - picture a cryptocurrency replacing the federal reserve, VISA, the european central bank, brick-and-mortar bank branches and credit unions (partially), etc. It couldn't replace everything, and new things would become necessary, but I think there is potential (even if small) for it to provide enormous value at least on the order of its energy consumption.
Traditional ways of doing all those things are faster and cheaper than blockchain.
Transaction clearing between banks isn't particularly fast, but that's because of legacy legal issues more than it is anything technological. The actual transfer of large sums can happen very quickly.