I believe that the silly mask on the forehead confusion is a combination of what I have in the past called "the reduction funnel" in teaching concepts and an unfortunately worded question on an OW exam.
The "reduction funnel" is a concept I made up and explained back when I was teaching educational concepts. It is something I saw many times. You start with a big idea that needs to be communicated, and that big idea is well thought out in detail. You teach it to someone who teaches it to someone who teaches it to someone.... Before too long, the big idea is reduced to a couple bullet points, and sometimes it is reduced to only one or two points in a way that may totally contradict the original more complex concept. In this case, the big idea is that a panicked diver can be recognized by putting together a set of clues that include among other things, equipment rejection. We note that equipment rejection is often discarding a regulator. It can also be rejecting a mask. the mask might be pulled down. It might be shoved off the head in an upward direction. If it is pushed upward, it might come off, or it might stay on top of the forehead. Once the big idea has gone through the reduction funnel, we are left with the simple statement that having the mask on the forehead is all by itself a sign of panic, a statement that is actually contradictory to the original big idea.
The old PADI OW course did teach the big idea, and it had a question on the final exam that talked about signs (plural) of panic. Unfortunately, the wording was such that, although technically correct, it made it very tempting for instructors reviewing course material prior to the exam to "remind" students that a mask on the forehead was a sign of panic. I imagine several million students took that exam over the years.