G never meant speed, you have Gb, gb, gb/s(which is gigabit/second) and GB/s (gigabyte/second). This in itself was marketing nonsense made by network providers to put bigger numbers by using a measurement
And FWIW, docsis has been around for a long time and is basically meaningless for normal end users. It’s the protocol that your modem/router uses to connect to the CSPs network. You only need to know what it is if something goes wrong or you’re studying networking