I could not go to the above given url, I got an error. Sometimes harmonica tunes are notated that way, the number cooresponding to the specific hole in which one would blow or draw to find the note of the melody. OR, I have seen something numbered like that, but without the - (minus sign) symbol, in turn of the 20th century booklets which accompanied the instrument with which it came, such as a banjo, or ukulele, or whatever. Each chord diagram which represented a chord or fingering, coresponded to a specific number for that diagram or figure on the page, but I think what you've found is for the harmonica, and does not represent chords to accompany the song.