Pretty much this. But the point is that a bitflip would be like, your CCD was supposed to read out value 0b00000 = 0 but due to cosmic ray interference, it read out 0b10000 = 16 instead.
Instead, what's happening in GGP's experiment is that actual electrons, created in the bulk of the active silicon region by a passing cosmic ray, are getting detected by the CCD, and it will (correctly) read out some value between 00000 and 11111, depending on how many electrons it saw. In principle you can actually make a histogram of these readout values and observe the Bethe-Bloch distribution of energy loss for ionizing particles through the (very thin) bulk of silicon! On the other hand, random bit flips (which are much rarer!) would just give you a random distribution of the numbers {00000, 00001, 00010, 00100, 01000, 10000}.
Instead, what's happening in GGP's experiment is that actual electrons, created in the bulk of the active silicon region by a passing cosmic ray, are getting detected by the CCD, and it will (correctly) read out some value between 00000 and 11111, depending on how many electrons it saw. In principle you can actually make a histogram of these readout values and observe the Bethe-Bloch distribution of energy loss for ionizing particles through the (very thin) bulk of silicon! On the other hand, random bit flips (which are much rarer!) would just give you a random distribution of the numbers {00000, 00001, 00010, 00100, 01000, 10000}.