Skimming through the article this looks like better signal processing coupled with the usual sensor fusion (from accelerometers and other sensors).

My knowledge of location systems only extends so far, but from what I know 3G, 4G and WiFi have not introduced anything particularly remarkable here. Wifi APs and various BSs are used as beacons (a la Skyhook), but their role doesn't extend much beyond that.

Anyway, there is still hope that 5G or some IEEE standard will make a difference here. They could perhaps provide something akin to a ground satellites, maybe at a very low frequency (to get past obstacles), or/and perhaps using UWB (helps with multipath, TOA determination). And then maybe we would have zeroish-time-to-fix, indoor-location on cheap, low-power devices.