HSV 1 genital infection is almost always passed through oral sex. The IgG test misses 30% of HSV 1 infections so him testing negative for HSV 1 cannot be counted upon. Also, sometimes people use the wrong test to look for HSV 1 antibody so that’s possible also. I would put my money on you getting HSV 1 from the person who gave you oral sex. That’s an educated guess, not necessarily 100% certain.