Pistons can be powered by a torch from 2 blocks above. Unrelated to Block Update Detection.

Place a torch 2 blocks above a piston. The piston extends. This does not occur from the side or bottom, it only extends when the torch is one block away, as intended. This is also not related the "Glitch adopted as a feature" that makes Block Update Detector switches possible, as the behavior is entirely different. BUD switches require diagonal power and a block update to change the piston, this is completely disconnected power and does not require a block update. This also does not occur when using any other power source, such as powered block or levers.