You have to remember the sensors rarely take up the whole area. The blue all the way around the sensor is not the sensor. If you measure edge to edge it would be APS-C, I included the actual numbers according to photoshop, ignoring the green it is definitely G1X sensor size. Zoom in check it out.
But what if your measure of 43mm is in the wrong place? Shouldn't it be on the outside edge of the lens where most other filter rings fit?
look how the lens cap is attached.. that is where the filters sit.
otherwise the sensor would be even smaller .. if the outer diameter is 43mm.