If someone is a drunk, they aren't being responsible. There is NO such this as a "responsible" alcoholic. There are functioning alcoholics, who can go to work and do all the other needed things. There is no responsibility about someone slowly killing themselves with a substance. BEING in addict is letting oneself and everyone around them down. Being able to preform tasks does not mean that they do and would choose their drug over everything else, in a second.
My guess, is he's been an alcoholic for some time. Al those years and you need more and more to feel it. Addicts are very clever, in how they can hide it publicly. He's probably braking now, and at a stage where it's impossible to hide, deny, or be clever about anything.
He wasn't a known alcoholic to US, the public. Think of all the celebrity and musician deaths that seem shocking, because the public didn't know about the addiction.