That sounds odd - I wonder if it was a relic of your local infrastructure. I used my own DOCSIS modem with its own firmware on Comcast around the same time. It was a generic Arris Surfboard.
Comcast's list of approved devices includes (or used to at least) some of the more common Arris Surfboards; I also used one when I had Comcast service. You probably also used one that was 'compatible'.
