I have no idea about Babymetal, but the type of music he is refering are songs like the Beatles "She loves you" with the "yeah yeah yeah." Other examples would be "Please Please Me" or "It won't be long". You hear it a lot in black soul music from those times.
And yes, he means the chants but I assume also specific parts you find a lot in idol songs. Best example would be a fast song, with a sudden slow interlude. Here people kecha (hand movements towards the singing idol). As you are familiar with Passpo, "Love Diary" with it's clapping, "Mr. Wednesday" (uh-uh), "Honey Dish" (chu chu chu, kyu kyu kyu).