5G in the router refers to the 5Ghz or 5 Gigahertz frequency range which has been in use for Wi-Fi technology since some of the earliest versions of WiFi, this is a completely different technology to 5G Mobile where 5G indicates the 5th generation of the technology.
Wi-Fi (Also known as WLAN):
https://en.wikipedia.org/wiki/List_of_WLAN_channels
Mobile:
https://en.wikipedia.org/wiki/5G
Further info can be read at the links below:
https://www.howtogeek.com/398620/whats-the-difference-between-5g-and-5ghz-wi-fi/
https://au.pcmag.com/feature/60170/5g-vs-5g-e-vs-5ghz-whats-the-difference