1) Devices can communicate with each other. Then they are not limited by the Ethernet uplink bandwidth.
2) The UniFi APs can also mesh. This means you can also pass on part of the uplink to another AP via WLAN. Maybe even your home server is connected to the WLAN and not only to 1GBit Ethernet.

WLAN transmits the signals to several devices on different frequencies. These 2400 Mbit/s are achieved by adding the two transmission rates of the 2.4 and 5 GHz frequencies together. If a WLAN router then communicates with several devices at the same time, the specified values that it can transmit can actually reach the maximum.

I am not a good on technical questions but this is the best wireless AP I have ever had. I have flooded the whole apartment block with Wi-Fi.