The second article notes that the 5G tests are being conducted on the 28GHz Ka microwave band. They also note that they're using a 64 element antenna array.
While those upper microwave bands are great in that you can get very wide channels (possibly hundreds of megahertz wide), their downfall is that they are incredibly line of sight restricted. This is compounded by significant atmospheric absorption. That's why many broadcasters on the band tend to use highly directional antennas. For omnidirectional use, you're going to have to deploy a lot of picocells.
Also for their tests, are they using the large number of antennas for MIMO beamforming (additive RF amplification), MIMO spacial multiplexing (parallel RF feeds slightly out of phase of each other) or old fashioned directional transmission (or a combi of all three?). How much additional cost is that? Even with fractal antennas on short wavelengths, how many of them can you fit in a handset?