Technically, he did not call them the same; he only said, " Should I call this, referring to his COA cladded hand, Tekkai." He probably did it because they work similarly and that he's fighting a Rokushiki user. Tekkai works completely different from COA:
So, unless you think Rob Lucci is a less skilled COA user than Amazon Lilly fodder, armament haki isn't Tekkai.