They said said the blockchain is "easier", not that cash is untraceable. It would require the participation of innumerable businesses to properly track cash; as it is, they function as a huge network of crypto tumblers.
You can trace when/how it was printed, but not who owned it.
You can't track all transactions done with cash, you probably can pick a bill from 10 years ago and locate the bank it originally came from but you can't know all transactions done with that bill.