(someone) got mixed up and (did something)
To "get mixed up" means to confuse two or more ideas in your mind. Usually when you "get mixed up" it means that there are choices that you make a mistake and accidentally switch. For example,
I got mixed up and took Highway 50 South instead of North.
You tell what you did when you were confused with the phrase "and (did something)":
They must have gotten mixed up and tried to use Version 2 instead of the newer version.