That is a supported living home. The extension is almost certainly to have a bedroom for at least one of the carers to sleep in overnight. If you are correct @Neighbourmystery that the service usar is physically well, then he almost certainly has a severe mental health problem, but one that means he is only a danger to himself, unless his home is extremely secure.
The reason why he has moved so far from the health service that has funded the house move - although I would have thought that the buying of these properties would have been the responsibility of the council area he used to live in, not the health service per se - is possibly due to one of two frequent reasons, they are probably the most likely ones, as to why he has moved so far away from his previous area.
One is that where he lived before is no longer a healthy environment for him. Perhaps he knows too many people who wish him ill, sadly this often includes at least some of his own family members. Unfortunately, as you must know OP, there are far too many people these days who are scared of whatever it is that they don't understand. It seems like an increasingly, and alarming fact, that those who fear something, or someone, without even knowing whether they are a danger to anyone, apart from maybe themselves, are potentially much more dangerous than the person with mental health problems.
The other likely scenario for moving a very vunerable individual many miles from their previous home, is that they were originally from the area they are now residing in, and may have been moved away from because during the early days of their mental health crisis (please remember this is all supposition on my part) they were moved for treatment to somewhere else within their own country - I will assume England for now, as different countries within the UK have slightly varying rules and regulations, and I am more experienced in the English format - as specific residential mental health facilities are few and far between, and patients are often sent to one many miles from their own communities because there simply isn't a suitable placement any nearer to their original home.
I hope that my suggestion, which is really the same as many of the other posts by pp, has helped put your mind at rest, and OP, it is very normal to speculate about differing patterns, those out of the ordinary to us as individuals. But the danger comes when neighbours, family's and friends, etc. start gossiping - including sharing on social media, especially while using real names and places - about what the reason is for some unexplained occurance within their own daily sphere. So asking here about it was probably one of the safer options, but please do heed nearly everyone's advice, to not start chatting about your 'interest' in real life.