It's a belief of some advocacy groups, like AA and such.

In real life, there are lots of drug addicts and alcoholics that managed to recover for the rest of their life just fine, including drinking in moderation for social reasons without relapsing (as opposed the teetotallism stance advocated by said groups).

Not to say it's a bad thing to drink after recovering from alcoholism, but wouldn't that just be managed addiction?

My uncle is an alcoholic, but has managed to drink at a reasonable level (not healthy, but doesn't socially harm him, e.g. drink driving, losing a job) for the past few decades. He'll crack his first beer at 10 AM, but manages to keep a good level of control.

>Not to say it's a bad thing to drink after recovering from alcoholism, but wouldn't that just be managed addiction?

Not any more so than drinking before alcoholism is "managed addiction".

If you can manage it and drink whenever you want after being an alcoholic (e.g. not drink for weeks, then drink at a party and then again not for weeks, and have no withdrawal effects when you don't drink) then you're not addicted anymore.

Addiction is not just a chemical dependency. The context in which you use the substance matters. Your personality and past behavior matters. This friend, in particular, took partying to an extreme. Not one drink but twelve drinks and blackout situations. Not just drinks but drinking and drugs. A lot of people who do not know her history will innocently say something like "We're going to happy hour" or "Just have a drink, it is the holidays." She knows though that, for her, the likelihood of that one drink turning into passing out at 5AM after an all-night rager are dangerously high. This is why I say there is no such thing as a former addict, as you can throw everything away with just "one".

That may be 100% true for her, but to say there is no such thing as a former addict, it would have to be true for everyone, which it isn't.