When someone says "Maria is either at home or in the office" they usually don't mean that she can literally only be at those two locations at any time - even a terminal workaholic loner would go for a coffee occasionally and would spend some time commuting from and to that office.
Yet on to apply the strict logical reasoning the rest of the article uses, you'd need that exact kind of literal interpretation where you can conclude that if she's not at home, she must be in the office.
In reality, when someone says "she's either at home or in the office" what they mean is that the probability she's at any of those two locations is vastly greater than the probability she's at some other place.
I think this is why today we're doing more formal reasoning in terms of probability than in "pure" logical statements, because it lets you capture those kinds of fuzzyness much better.