It’s a Dark Jedi, actually, not a Sith Lord. And yes, I realize I’m being pedantic. ;-P
No you’re not. Sith have rules, a creed, a recorded history, etc. The term “Dark Jedi”, while possibly synonymous with any dark force user, doesn’t necessarily refer to someone who belongs to the Order of the Sith.
It’s not pedantic. It’s geeky. But geeky is cool now.