The point still stands, though: the app doesn't digitize the sheet music, it displays it from sources that have already digitized it.
Unless the scores are beying keyed in by hand, the actual digitization of the sheet music is basically a specialized OCR: http://en.wikipedia.org/wiki/Music_OCR
Doesn't it mean it digitizes the "process" of sheet music -- the whole thing from notes to someone playing it? Not just the sheets with the notes on them. This meaning for "the app digitizes sheet music" makes sense, at least for me.
Unless the scores are beying keyed in by hand, the actual digitization of the sheet music is basically a specialized OCR: http://en.wikipedia.org/wiki/Music_OCR