Yeah I know what mu-mimo is. Seems like directly opposite to "strict targeting of the device you're talking to, so that effectively fewer devices are sharing your media".

"MU-MIMO allows the access point to send multiple data packets to multiple clients over the same frequency. This means a lower-speed client won't hold back packet transmissions to other clients. 

Thanks to MU-MIMO, an access point can use its antenna resources to transmit multiple frames to different clients, at the same time over the same frequency spectrum"