Photo 1: Despite the circumstantial evidence, the millipedes did not damage this carrot; they are taking advantage of previous damage.
A 2012 research article in the Journal of Applied Entomology looked at the potential of millipedes and wireworms to attack carrots (also sweet potatoes). They found the presence of the millipedes was associated with wireworm damage to carrots. The millipedes themselves were not causing damage but were there as a result of preexisting wireworm injury. That is also what is probably happening with the presence of millipedes in the potatoes. The millipedes were not damaging the tubers but were there because of other damage (probably wireworms).
Fortunately wireworm damage is not common in home gardens and this kind of injury (as well invasion by millipedes) should not be a problem very often.