I think he said that because the new iPhones and Androids support the new T-Mobile LTE Band 71.
https://bgr.com/2018/06/06/t-mobile-coverage-fastest-network-vs-verizon-2018/
A little under one year ago,
T-Mobile turned on the first site in the US to use its 600MHz frequency, a low-band chunk of spectrum that provides much more consistent coverage, especially indoors or in rural areas. Building out the new network on a nationwide scale isn’t a simple process, but the company just announced that it’s now up and running in 900 cities and towns across 32 states, a huge achievement in just 10 months.
Of course, as with everything in life, there’s a catch. The 600MHz spectrum — which you’ll also hear referred to as Band 71 or Extended Range LTE — was until very recently used to broadcast analog TV into homes. T-Mobile is the first network in the world to use it for LTE, and as a result, the majority of phones don’t support it yet. That’s changing fast — recent flagship Android phones from Samsung and LG are compatible — but for anyone using an iPhone or an older Android device, all of T-Mobile’s efforts to roll out its 600MHz network mean nothing.
