Some people think that by offering an explanation to their users during a usability test session, it alleviates the confusion and the pain that makes users confused.
That is not the point!
The point of user testing is testing the design - not making others feel better. While it is necessary to accommodate for scheduling and to be polite, making users feel better because of confusion and bad design is not the way to go. In many of my sessions, I've had users do things that were not intended for its purpose. Certain clicking behavior and sequences weren't as I intended. It was because of the lack of better design - not the lack of the user's understanding of the design.
To explain to the user what the design was all about defeats the purpose of the usability test. It becomes a demo and not a test. And when this happens, the results become skewed and unusable.
So what happens when a user complains about the design or they're misunderstanding the product? It could be that you've chosen the wrong user. Most likely, it could be the design isn't up to what the user expects.
That's why testing and design needs to be iterative - to allow for incremental change that is better than the last iteration.
And most of all, have faith in your users. Acknowledge all their feedback. You can later filter out the feedback that are less relevant. And don't make the user feel like they don't know what they're doing. Always lead it back to the design and apologize for the design - not to yourself or any other person.
By removing yourself from the design and the test session, to remain objective, is the best thing you can do to get the best results - and without bias.