Such errors are rare by experienced STD clinic professionals. You can stop worrying about it.
I saw a professional today at an STD clinic, and he said that it is very unlikely it is a genital wart or HPV and said it is most likely a normal skin bump of some sort. He was "almost certain"
Since you gave the same information I am inclined to believe that it is true. It is always a little disconcerting that he couldn't be completely sure. Do errors occur usually in a visual inspection?
Welcome to the forum.
On the one hand, you are at risk for HPV. Not because of your genital bump, and not to imply you are at high risk. The simple fact is that almost all sexually active persons catch genital HPV at one time or another, and most people probably have several infections. The frequency of HPV is almost as high in people with conservative sex lives (e.g. under 10 lifetime sex partners) as those with very active lives (100 or more partners).
So on that basis, you can assume you have had it. You may have HPV now. However, from your description I am inclined to believe your single penile bump is not a wart; as you imply yourself, a single lesion and a smooth, round lesion is not likely to be a wart. My guess is that this is more likely to be a fibroma, a prominent sebaceous gland or hair follicle, or some other normal variation in your penile skin.
But of course there is no way I can be certain; the only way to sort this out is to be professionally examined. So I suggest you do that. Feel free to report the outcome after you have been examined, but until then I really can't help. In the meantime, try not to be worried. Even if you have a wart, you should consider that a very minor medical condition -- an inconvenience, not an important health threat. So either way, there is no basis for serious concern about it.
Let me know what is found. In the meantime, I hope this has helped.
Best wishes-- HHH, MD