[Chibi-Chan]

My point was that it's for sure that she is able to read sheet music. It's not relevant how many times she used the keyboard or was just recording herself humming the melody. Humming 7/4's title is somekind of a "joke". The "Humming" part is a references that she was just humming the melody but the "7/4" is the actual "joke" behind it. People who looked into the sheet music of the song and are able to read it know what I mean. Ayu tried to be funny here. She wouldn't be able to make such a "joke" with the title of the song when she woudn't be able to read sheet music - in this case the title of the song would be only "Humming".