My instinct would be to say there are either:
* two first cousins, both Jean Christoph. One born to Jean Nicholas, the other other Jean George. In this case, the annotation in the marriage helps distinguish them
* the marriage annotation has a mistake, and it was meant to say Jean Nicholas.
Both are plausible to me, but the alternative, that it's referring to the grandfather seems less likely. Based on what I've seen in these records, they always mean the actual father.