I thought the deal was with Lea? Also Jim has said in the past that what she did was merely confidence building and no power per say, I also thought that the reason why he was declared a warlock was because he killed with magic when he killed Justin.
I think Jim was referring obliquely to Harry becoming Winter Knight (the guy interviewing him had just finished White Night, so Jim was being a little bit carful about spoilers for him)- he did specifically mention Mab, not Lea.
The Wizard/Warlock/Sorcerer mentions in regards to Harry were about what class of character he would be if you tried to make him in Dungeons and Dragons. Jim’s point was that he uses the above terms differently in his works than they’re used in D&D.
This is out of universe stuff, the Daniel I mentioned is the name of the person interviewing Jim, not Daniel Carpenter FYI. Sorry if that was confusing.