I'm not saying that what you're saying isn't possible, and could very well be what happened, but that doesn't change the WTF factor when something is supposedly not going to go away without surgery.
Well, yes. The issue here is "supposedly". I've had a bit of experience dealing with the medical system, and (at least in the US) there's an epidemic of overconfidence to the point of idiocy among doctors. This manifests in several ways, such as:
1) If the tests that ONE DOCTOR thinks are worthwhile come back negative: "There's nothing wrong with you, it's all in your head." Even if there are significant possibilities still not excluded. (Note: in any remotely complicated presentation, it's extremely rare that two doctors will think of the same set of tests to run... and many doctors don't actually know the proper best-practices for testing for various conditions, even within their own specialty.) On the flip side of the issue - if a test comes back positive: "That's the issue!", even in cases where false positives are incredibly common. This is overridden only in very specific circumstances, where the doctor is trained to question a specific test as routinely giving false positives - their statistical training is often shallow enough that they cannot extend this past the explicit guidelines.
2) Once a doctor decides that they can treat something, they will often exaggerate the need for treatment, saying things like "This will not go away without surgery" even in cases where as much as 10% of such phenomena do. Or more. Think about how NEW physical therapy is as part of accepted medical practice... and how many illnesses are best treated by physical therapy, where doctors had always resorted to surgery before. Chronic lower back pain has now been shown by scientific study to have essentially identical outcomes by surgery and by physical therapy - yet, if you asked a surgeon whether the surgery was beneficial, they always said yes. The best then went on to point out that the added risk and complication might balance out the benefits - but they always held that there was a significant improvement in the best outcomes.
3) Confirmation bias. Once a doctor or technician highlights an abnormality, it's remarkable how many people will find the same thing when looking at the data - even though, provided with the data and NO information on the diagnosis, they would not have found the issue. You know how scientific experiments are usually held to the "double-blind" standard? This is specifically invented to limit confirmation bias - because it has been shown, over and over again, to be incredibly powerful. In a noisy image, we tend to see what we expect to see.
In other words - spontaneous remission is possible. So is a mistaken diagnosis, even with confirmation, unless you have reason to believe that the second technician read the data blind to the previous technician's work. Personally, I suspect that the surgeon strongly exaggerated their case - as they often do. "This NEVER goes away on its own" may mean that the likelihood is less than 10%. Or less than 1%. Or even 1 in 10,000! Unless the disease is extremely rare (in which case any such statistics are questionable due to a small sample size), 1 in 10,000 still means that it happens to plenty of people in the United States alone.