I don't know the full story with Christian but he was lucky enough to be doing both by the mid 2000s to early 2010s. I think he was a producer for Naughty America which gave him work with a lot of women. At a certain point he pretty much stopped working with top female stars and went straight to almost exclusively trans, bbw, and older female stars.
As far as trans women, he pretty much spams every new chick with a twitter before they get a chance to make any real connections with other girls in the industry to warn them about him. That's why pretty much every new girl that goes to the pro-porn side has their first scene with him.