No. As long as there is a non-zero amount of plays(not sure how it works if you do not have plays selected for only one playbook like offense/defense) selected the AI should not add plays. The only time it has ever added plays for me was when I forgot to set my plays(did this in MLB League after allocation) so I had zero plays selected, cleared all selected plays and did not add any back, or loaded the AI's recommended plays.
I just recently hired new coaches in several leagues and defensively all my plays stayed the same as I didn't change my defensive playbook, but every offensive playbook was changed and no plays were added. It only kept the plays from the previous playbook that were in both offensive playbooks. I suspect somehow one of the options above happened, but would still submit a bug report/PM JDB about it just in case so it doesn't happen to you again if you can help it.