Well of course Yusuki told you to only feed his food to the frog. He is a businessman and makes money every time you buy the food.
A varied diet is alway best. It keeps the frog from getting bored with one specifi food item which they will occationally. Give the little guy a variety. You don't want to run out of the food and the have the frog go hungry while you're waiting for it to arrive. It takes over a week sometimes just to get one bag in the mail and if demand is high you may wait longer.
Offer him crickets, Night Crawler chuncks, Waxworms(treat only), and Hornworms(Goliath Worms also a treat). Don't forget to dust with calcium D3 and a good reptile/amphibian multiviamin.