Well that's some amazingly stereotypical statements regarding homeless people. There's all kinds of things that can happen in someones life that can lead people to that point. Even with the drugs and alchohol not everyone ends up losing their teeth, and even some of the most down and out people will still do what they can to clean up everyday.
If he's legit and really is trying to get his life together then it's very possible that he could have access to a shower and even clean clothes. Either from a shelter, or even friends. Even the most down and out people can still have friends that help them out with little things like that. A lot of times other poor people are more likely to help people like that out than well off people would. They usually can't do much to help someone get back on their feet because they're struggling to get by themselves, but they'll help with what they can.
I've seen people lose careers, businesses, and every thing they had due to drugs and alchohol, divorces, job layoffs, and many other reasons. Even without a drug problem, once you hit a certain financial level it becomes VERY difficult to get back out of it. If someone reaches a low enough level then tasks just dealing with the basic necessities to survive becomes all-consuming of their time.
Just because someone includes finding a place to clean up everyday or two as a priority doesn't mean they aren't still struggling just to survive. A lot of people can have amazing talents and circumstances can still take them down. Even if they bounce around shelters, soup kitchens, and even the occasional friends couch to sleep on they're still homeless. He might not even be completely homeless, but living in some slumlord's little substandard apt or hotel that you wouldn't ever consider living in your self. There's a lot of people living in places that are just a very small step above being homeless again. For many of those people it wouldn't take much to push them back on the street.
The list you gave makes judgements based on a bunch of stereotypes. You really can never tell based the type of things in your list. There's a pretty large variety of different type people that are down and out.
The story looks legit enough to believe the guy is struggling. I hope the exposure from that video helps get him another chance.