Over 100 simultaneous users is quite the success for a MUD back then and especially today. I also learned C by forking DikuMUD too, it was so accessible and easy to tweak.
It was indeed quite the success, but there were a number of MUDs in the 90s and 00s that would hit 100+ regularly. The MUD I mostly played at that time (WoTMUD) was hitting 200+ regularly for awhile.