Aha, this means that the filming was done in the first week of October. I didn't know Maimi pushed her voice that much during the concert.
☆ 9月24日 - ℃-ute Concert@Zepp Sendai
☆ 9月29日 - Buono! PV (Maimi had already lost her voice)
☆ 9月30日 - ℃-ute Concert@横浜BLITZ・昼夜
☆ 10月1日 - MUSIC FIGHTER recording (She implied it was because of yesterday's concert)
Maybe she just had a cold and didn't want to admit it unless she lost her voice from the september 24th concert or rehearsal or something.