I think getting HSV from a very short genital to genital contact with no movement is extremely unlikely. it sounds to me more like a real friction burn from masturbating with boxers on, especially if the seam of the boxers were in direct contact with the area of the abrasion. It is also possible to acquire HSV from oral sex and that would be HSV 1. You did an IgG test in 2017 and these are the only contacts you’ve had since then? Have you retested?