I read some more about this on internet.
In one article, a coroner explains that it is not as rare as we think to find people that live next to the body of a deceased loved one, be it a husband, wife, parent or child.
He says that some people simply cannot realize that that person is dead, the reality does not kick in at all, and others do realize it but are in denial simply out of attachment, they can't part with the physical remain.
Usually the smell alerts the neighbors. In this case, the neighbors thought that it was because of the dirty garbage that the house was filled with.
If the smell does not give the alert, it may be the family that looks for someone that has not appeared in a while. In this case, the family of the deceased had stopped all contact with the deceased, so they obviously were not looking for him.
So, it appears it is not rare to find such cases, but they usually are discovered within a few days, what is extra ordinary here is that it lasted for one year!
The owner of the place where they lived reverted to an expulsion of the "couple" because they did not pay the rent for a year. And thus he discovered the body while coming to the house.
Now, if they had continued to pay the rent, this could have gone on much longer...