In C#, when passing strings between classes, it's important to understand that while strings are reference types, they are immutable, meaning that any modification creates a new string rather than altering the original. The issue arises in the provided code where Class B does not have access to the updated tooltip text from Class A because it is only receiving a copy of the string at the time of the method call. To resolve this, Class B needs to maintain a reference to Class A's tooltip text or be updated each frame to reflect changes. Additionally, the confusion regarding static versus instance methods indicates a misunderstanding of object-oriented principles, particularly how instances of classes are managed in Unity. Properly managing references and understanding the lifecycle of Unity scripts will help in resolving the tooltip update issue.