Unfortunately, many folks think that once an addict, always one. While this is true for some folks, it certainly isn't true for everyone. You really can be "fit" to drink again.
If they don't get treatment, were they ever properly diagnosed? As I understand it, "drinking (way) too much" is something a good number of people in their 20s do, then they cut down without any particular problems. That isn't alcoholism, it's just drinking too much. Even the urge to grab a glass of wine to relax, when it's just a habit, isn't an addiction.
If they had trouble quitting, such as withdrawal symptoms, and only managed to do so after hard attempts, then they don't really need to be diagnosed.
Other than that, the line between alcoholism and drinking too much is really blurry, if it exists at all. Some people manage to function perfectly and be OK while drinking heavily throughout their lives, and are not considered by others or consider themselves alcoholics.
Btw: "One of the most interesting findings, as far as I'm concerned, was that among remitted alcoholics (link is external) the average amount of drinking was around 1.3 drinks per day with a lot of variability, a little higher than that of moderate drinkers (0.8 drinks per day) but lower than that of heavy drinkers (4.0 drinks per day). I see this as a little more proof that people who met criteria for alcoholism at one point don't necessarily abstain forever and don't necessarily continue to have drinking problems (per Moderation Management (link is external), spontaneous remission (link is external), or some other means of stopping their alcoholic drinking)."
Besides, non-diagnosis happens all the time, and is more common when folks either can't afford healthcare of if using healthcare means they put their jobs at risk. People have depression and don't seek treatment, but that doesn't mean they aren't depressed. Folks break toes without treatment. People clean up from harder drugs and we don't question if they were really addicted or not most times. It doesn't mean their toe wasn't broken, simply that they didn't get it treated. Medical-based treatment is expensive and not everyone can afford to get a proper diagnosis.
Going to AA meetings isn't a diagnosis either: They don't require any of that. I can go into AA as an occasional drinker and simply lie about it. If I get in legal trouble during on of those occasional drinking sessions, I might be forced to go.
The uptake of treatment and a proper diagnosis doesn't mean someone isn't addicted, simply that they didn't have official treatment.