If the administrator wants to map an SSID to only one of the radios, that can be configured in the WLAN settings.
For instance, if all devices on that SSID are known to be 5GHz capable instead of relying on band-steering which would 'nudge' clients but will not guarantee they dont use 2.4GHz it could be enabled on just hte 5GHz radios.
Similarly in a retail store there might some old point of sale devices which are 2.4GHz only. Mapping this SSID to 5GHz would waste airtime on 5GHz (from beacons and other management packets), so having this SSID being serviced on just the 2.4GHz radio can be useful.
To configure this, choose the radios configuration item under wlan basic configuration and set it one of the bands instead of hte default of being on both 2.4GHz as well as 5GHz: