Dev team members are responsible for decision making during the sprint


The development team is indeed responsible for all the progress during the sprint. Once the sprint backlog has been determined it falls solely to the development team to make it happen. No one outside the team (Scrum Master, Product Owner etc.) may interfere with the work.

Most of all the development team decides how they want to proceed with the work. The what is already clear since it is displayed in the Sprint Backlog.

If other people do make these kind of decisions for the development team the progress will suffer. Often times it might happen that the Product Owner or external management think that it is their area of expertise to suggest specific actions to reach the sprint goal. This is not the case and the Scrum Master has to ensure that the development team has the freedom to act and no one interferes with that progress.