I saw the "Every kiss begins with Kay" commercial and it says that someone made the diamond cut. Is this true?

You may have misinterpreted or heard wrong. 'Made the diamond cut' could mean two things, diamonds are the hardest surface on earth, therefore, they can cut; that is why they are used in mining applications. Kays would have had nothing to do with this. Or, 'made the diamond cut' meaning invented the first diamond cut, meaning a very risky procedure of cutting a diamond in the
Rough into a cultured piece of jewellery, there again, Kays would not have initiated this.

Diamonds (my favorite jewel ;) ) are mined in an uncut state. To get stones that can fit and are of jewelry quality, they have to be cut from the original stone.

I don't know if Kay employs their own cutters or buys from jewelry whole-sellers.

Curious though, why this matters to you. .

OP is 9 years old and asking a ton of questions.