Were you the giver of oral sex to this new partner? If yes, did you share that information with the provider that you saw?
It could be HSV but if so, I would expect possibly external oral lesions as well though that is not required.
I think I would recommend that you redo the HSV antibody test in about 6 weeks and see what happens. I think it is far more likely that you have a bacterial infection of the throat. If you were not the giver of oral sex to this person but only did kissing and intercourse, HSV is also a possibility.