Diagnosed as 'fine' - why am I still concerned?

(This is actually an update to a previous question where I was advised to have him diagnosed)
Hi. I recently posted about a friend, let's call him Mike (70), I am convinced has dementia. His doctor yesterday told us he was 'fine'. But I have been in this situation for about 7 years now and I disagree. Just a few points: A.) the doctor did a 3-question mini-mental and Mike answered correctly (except the day) but with hesitation. B.) Mike lied about taking his BP tablets; he has taken 3 weeks' worth over the past 3 months (I checked before we left). C.) He lied about 'coping', saying he does all his own ironing, etc. In fact, he eats ONLY takeouts, does no washing and baths once every two months (he showered before going to the doctor, the first time in two months). D.) The fact is he has had to sell his house to pay debts relating to non-payment of utility bills. E.) Asked what he 'does', he replied reads, goes for walks, watches TV and keeps busy. In fact, he reads newspaper (not books), does no housework or cooking, walks 20 minutes a day, goes to pub every night, stares into space. His TV has been broken for the past two or three months. His laptop lies on the floor with a broken screen, so he uses the TV screen to get onto the internet where he accesses various webcam sites and porn.

I did an online test as a friend for dementia. He scored 15 (1 to 5 being 'normal').

So, am I wrong? Is this just laziness/ depression (there is a good possibility of this). Or is just still at a stage where he manages to hide it? Or is the doctor an idiot?

Regarding the doctor, to be fair, it may well be that Mike is actually functional and the doc thinks it's not at a point where anything needs to be done. Plus, the doctor must have noticed how dishevelled he looks.

My decision right now is to walk away. To take the odd meal and be a friend, e.g. invite him for a barbecue, ask if he needs stuff. But NOT to go and fetch his medication, only remind him when it needs renewing, not chase him up on it every few days. I have done what I can and now it is up to his family. (Sons who live up the road visit about every 3 months or so. Sisters pop in and rant at filthy house but think he is just lazy. I am the one to take him to doctor, for X-rays, to the shops, etc. NO MORE. He told the doctor he has no problem going to the mall. In fact, he hasn't been for a couple of months. Eats takeouts and buys coffee locally. Has no need for cleaning materials. Even admits his underpants are so old they fall down around his waist.).

I have spoken to pub friends and neighbours: 'Hell. Mike's been wearing the same shirt and jeans with a hole in the crotch for two weeks now.' 'I asked Mike what he and James had been talking about last night but he couldn't rememember he'd spoken to James.' 'His house smells awful.'

Thanks in advance. I guess I want confirmation that it's OK for someone else to pick up the reins now. We were an item for a while but are just friends now. I work from home and, just starting a new business, don't have time to be a carer. I also have an 81 year old mother who takes a bit of my time (she is GREAT and fit and fine but needs help, for e.g. taking car to mechanic, and I like to spend fun and quality time with her going out and having meals. Who knows how long she has.)