Must be co-incidence, much like the following ...
2012 - 3 NRFL Prem teams in Quarter-Finals - two drawn together (Central vs Eastern Suburbs.)
2013 - 4 NRFL Prem teams in Quarter-Finals - all drawn together (Melville vs Birkenhead, Waitakere vs Onehunga.)
2014 - 4 NRFL Prem teams in Quarter-Finals - all drawn together (Melville vs Onehunga, Central vs Hamilton Wanderers.)
(The Cup is an 'open draw' from Quarter-Finals stage which means that, theoretically, any team can be drawn against any other.)
Melville weren't Prem in 2013. Actually, they weren't Prem last year either.