Yep. Especially teacher’s unions.
My guess is that maybe this “teacher” is a coach. Too many coaches are asked to teach other subjects that many of them are not qualified to teach, IMO. The only exception to that I ever saw was my high school algebra teacher. Smart as a whip and knew his stuff. He was also the basketball coach. He moved on to become principal and eventually school district superintendent.
In many states that's illegal, and can cost the district big time if it's discovered. The problem is that districts too often keep it quiet, and no one is the wiser.
The famous John T. Scopes (defendant in the TN "Monkey Trial" of 1925) was substitute teaching when he agreed to stipulate that he had "taught evolution", even though he had no recollection of mentioning it in class.
His main job? Football coach.