Anno Domini means roughly "in the year of our Lord" in Latin short hand. Little Willie was mistaking it for the name of another woman. My guess is that it was written as an attempt at humor.
Yes, it was part of a column that contained a number of totally unfunny jokes of sorts and a couple of dialogue only jokes like the Anno Domini one, which in fact, did make me chuckle, so I put it in yesterday's thread. I guess if I were a comedian, using it in my act, it would have been met with stone cold silence. Haha.