The funny thing is that beamforming isn't some laser that the tower can aim at people with.
The technique for tuning a beamforming signal is to see which antennas a signal is coming on (on your 100 antenna array), and then boost the gain/match the phase on those antennas to match. It's just linear algebra, not a cannon.
Also most wifi routers do beamforming, and apparently it's not new to 5g either. I think the new antennas are just better at it, using more antennas to make it more directional, and using better algorithms to make it faster and avoid interference better.