A swab test is conclusive. If the swab came back positive for HSV1 then that is what the sore was. HSV1 genitally is usually always spread by receiving oral sex from someone who has it orally. A blood test, the IgG, is only about 70% accurate after 12 weeks. It’s just not a good test for HSV1. I would believe the swab results.
The appearance of the sore about a week after the unprotected oral fits the timeline. Sounds like it was a very mild outbreak and HSV1 genitally tends to recur infrequently and doesn’t shed like HSV2.
To add to and support TooHip's response, the swab trumps the blood test. It's more accurate than the blood test. Because it came back positive, I would definitely conclude that you have genital hsv1.
FYI, you are still susceptible to an Hsv2 genital infection, i.e. you can still be infection with hsv2. You have genital herpes but not the typical variety caused by hsv2.
Additionally, 45 days post encounter may not have been enough elapsed time to get a positive reading on the hsv1 test, but as TooHip pointed out, the IgG antibody test for hsv1 misses around 30% of infections.