PBL emanated from a model used in medical schools. Learning occurs in small student groups. Teachers are facilitators or guides. Problems form the organizing focus and stimulus for learning. Problems are a vehicle for the development of clinical problem-solving skills.
New information is acquired through self-directed learning.
My own interpretation is that the teacher would not need to step in if the scenario was well designed for the audience who is solving the problems. That shall be the case for you. Don't look for me to step in on these two exercises. Our purpose is to have experiences with problems that can be used to help students learn mathematical concepts, principles, procedures, and skills. You should design several authentic projects each semester that will help your students learn to solve problems by using the appropriate mathematical concepts, principles, procedures, and skills.