I totally agree with Dr. Hook, and would have said the same.
That said, Dr. Hook literally wrote a book on syphilis, and I would absolutely trust him on this. He is definitely an expert.
FYI, Dr. Hook answered a similar question:
" In most situations however, if a syphilis blood test is going to become positive after an exposure, it will typically do so by five weeks after the exposure. The same is true for HIV and at 6 weeks, HIV tests are absolutely conclusive. The recommendations you received for re-testing are overly conservative. I am confident that your 11 week tests will also be negative. Please don't worry. "
"At 5 weeks your HIV result was more than 99.9% accurate. As for syphilis, there are fewer high quality data but my estimate is that the five week results are also at least 99% accurate. I have never seen or heard of an instance for either infection in which a result changed after 5 weeks."
So probably I am safe, combining the negative test with the facts that this was a very low risk exposure, and my lesion did not have the characteristics as a typical chancre.