Mignarde is in the very unusual key, for the lute, of E minor. This might be a wordplay on the title, since Mi is the musical note E. Dowland used this device in other music, most notably the song Lasso vita mia, mi fa morire, where the highlighted syllables outline the initial melody, dropping from A down to D.
There are quite a few incorrect notes in this piece, some corrected and overwritten, some not. Generally, they're out by a semitone (i.e. by one fret). For example, in the B major chord in the final cadence, the added dominant 7th A, which should be fret e on the 4th course, has been written as fret f.
How did this happen? It looks as though Holmes can't have been copying directly from a tablature source (unless his source also had all the same mistakes). He's unlikely to have been making an intabulation from an original in conventional notation, since such originals don't really exist. Most likely he was working from memory, but away from his instrument. An unusual key means unfamiliar chord shapes and fingering patterns: easy to go wrong. If he'd had his lute to hand, he would have spotted and corrected those mistakes.