Upon reading several chapters. I can safely say that what koby used in chapter 1088 was indeed advanced coc.
Here are the two reeason why not a single person can contradict:
1. There is 0 example of regular coc, or advanced coa or regular coa having signs of leaking haki from a fist or a sword BEFORE IMPACT. Every leakage of black lighting from any of the above only happens when there is a clash or when an object or someone is hit.
2 battle ship bag training does not train your armament haki since the rules are to not use haki or devil fruit ability. Which means the only version of haki that can actually increase with this type of training is coc. Since the only way to level up coc is for the person him or herself to level up as a whole.