I have no way of contacting the guy to ask him about his health status.

Oral sex is generally considered safe sex. It's not completely free of risk, but the overall risk is low for all STDs and zero for some. There are many possible cause of a "red patch/dot" in the penis, and the large majority of genital skin rashes and lesions are not STDs, so that aspect does not elevate your low risk. However, the risk of infection is not zero. Of course get medical care right away if you develop oral sores or severe sore throat within a few days (symptoms of herpes), or if an oral sore after 10-20 days (syphilis). Gonorrhea of the throat is possible, but usually causes no symptoms and testing would be necessary to rule it out. HIV is exceedingly unlikely, less than one chance in 10,000 even if he has untreated HIV.

Assuming no symptoms, for reassurance I would recommend a throat swab for gonorrhea testing, which is valid any time 2-3 days or more after exposure; and blood tests for HIV and syphils after 6 weeks. Chlamydia testing often is done more or less automatically along with gonorrhea, but oral chlamydia is very rare and it's not a serious concern.

In the meantime, stay relaxed. This was a low risk event and you can expect all these tests to be negative.

I hope this information is helpful. Let me know if anything isn't clear.

HHH, MD