Using the picture provided, when redstone is placed on/removed from the green wool, it causes the piston to update, even though no block touching the piston was updated.
Edit: The update persists even when the yellow wool is air.
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Redstone updates occur two blocks around any redstone related item turned on, placed, or broken unlike block updates which only occur adjacently. It has been like this for a while and it doesn't seem like it will be changed anytime soon.
WAI. See MC-108