It's even simpler. The official excuse would be "we didn't know that this person has dementia and/or other issues that could prevent them from giving consent. We aren't doctors."
Well, at least the police now has a simple way to search occupied residences. Arrest everyone who objects, one by one, for "interference with investigation" or for "disturbing the peace", until one of those who remain surrenders and allows the search.
In this case the guy who was arrested attracts no sympathy. But that's always how new laws and rulings are installed - on test cases that are open and shut, when nobody can defend the bad guy. Shortly after the same legal principle is used against everyone else.
Bingo.