5g is still simultaneous multiband just like 4g, but with more room for growth higher up. It will reuse existing spectrum for most traffic and allow coordination and handoff with small cells to allow higher frequency bands for faster speeds where available.

The majority of the devices in the world will rarely see the higher frequency bands for 5g though due to the range issues. If you look at it as a percentage of your day, you will probably be using 5g on the old bands for half or more of your day once deployed.

It really is a marketing stunt with some minor technical improvements in the background to allow for better division of spectrum on the towers to allow more burst traffic to more devices. Things like messaging and push notifications, and m2m for smart devices.