Boolean Logic and its logical operators just gather or separate things into neat piles depending on how you use them. The diagram at the left shows how the Boolean logical operator AND works. The area occupied by these two universes overlaps. Any documents containing just one of the two terms and not the other would be excluded. The fact that they are all present in a document, though, does not mean that they're linked logically or conceptually in any way.
False coordinations are common when AND logic is used.
All it guarrantees is that the two terms will co-occur in the resulting documents. AND logic focuses, coordinates and narrows a search. The diagram at the left shows how the Boolean logical operator OR works. The area occupied by these two universes overlaps. The Boolean logical operator OR makes the overlap complete.