I've had strong (8.5%+abv) IPAs go "blue cheese" on me while in the fridge... ever since then I never keep store-bought IPAs around more than a couple weeks because you never know how long its already sat around.
You had something else going on. This wouldn't be typical for an old beer that was kept under pressure and cold. Once a beer starts to "go bad" from age, it gets cardboardy and stale, followed by vinigary.
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