I was assuming that the folks doing the observing did not necessarily realize that all the previous triangles were right and this one is not.

In this case, the folks doing the observing do realize that this triangle is different from all those previously considered, but they downplay the significance of this fact, perhaps using the justification: a triangle is a triangle is a triangle.

(I'm actually not making this up as I go along. I had worked out this example some time ago to illustrate what I believe to be a widely-held false belief in finance. I believe that WAW is a good description of the thought process behind this belief.)