You're a student in the Pokémon school and you lived with Ash and Professor Kukui because you weren't from Alola and you lived in Alola longer than Ash. Ash was supposed to do a presentation on what he learned since coming to Alola for an open house the next day from Kanto and he was struggling until his mom arrived. After his mom arrived Rotom Dex offered Ash to do the presentation for him while they were hiding. You didn't need to do the presentation because you were in Alola linger than Ash and Professor Kukui didn't want to stress you out and make you talk in front of people. The next day during the open house at the Pokémon school Ash was doing the his presentation with Rotom using his voice. Mallow, Lana, Sophocles, Kiawe, Lillie, and Professor Kukui because Ash's presentation wasn't what Ash would say and everyone visiting for the open house didn't notice.

Ash/Rotom: doing the presentation Kiawe, Lillie, and Professor Kukui: suspicious of Ashs presentation Mallow: whispers hey Lana, does Ash sound like Ash? Lana: whispers Nope Sophocles: whispers Why do you think he's like this? Mrs Ketchum: doesn't notice Harper and Sarah: excited to see Pokémon Hobbs: doesn't notice anything suspicious