Because the transaction is created and signed on the completely "offline" (airgapped) cobo wallet device itself... and you only use your smartphone to scan the QR code off the cobo's screen and then broadcast the transaction.
Makes sense, but I couldn't find that information on their indiegogo or their website. They just keep harping on about how it has military grade durability - because apparently being able to work down to -20 degrees Celsius and being sand and salt resistant is more important that any actual technical details. I'm not sure who is trying to spend crypto deep in the middle of the Sahara or the Antarctic, but given your phone has likely packed in long before then, you wouldn't be able to broadcast your transactions anyway.
