Aw, don't feel bad. You didn't know.
And I know you don't want to feed anyone's addiction, but the guy most likely IS an alcoholic. He's sick. He can't live without the booze. You helped him cross the street. That's all there is to it. Does it matter that you helped him cross the street because he had to get a beer fix? Would he be more worthy of help without the beer? Your post implies that, but I would argue the guy is like anyone else with a serious illness.
In the end, you help who you want to help, but I wouldn't feel bad about it. He may not be trying to "play" you, he's just a sick old man who probably appreciates some assistance now and then.