Looking at a half circle and guessing that the "missing part" is a full circle is as much of a blind guess as you can get. You have exactly zero evidence that there is another half circle present. The missing part could be anything, from nothing to any shape that incorporates a half circle. And you would be guessing without any evidence whatsoever as to which of those things it is. That's blind guessing.

Extrapolating into regions without prior data with a non-predictive model is blind guessing. If it wasn't, the model would be predictive, which generative AI is not, is not intended to be, and has not been claimed to be.