There's brief 1 minute audio bite, in this link whereby Hudson outlines why they chose just the one friendly.
http://www.nzfootball.co.nz/all-whites-to-play-japan-in-october/
It sounds as much like getting the players back to their clubs a little early (as opposed to later if it was 2 games) at end of this window, and so thereby keeping the clubs onside for the all important November window (South American playoff games).
As Hudson states October can be a very busy time with various club comps - eg MLS playoffs start late October, and AWs now have up to 4 players (Musa, Marinovic, Colvey, Boxall) who could be involved - so care needed to work with the various club coaches, if asking for a few favours like an early release for November etc.
Hopefully Reid is available for this Japan game - surely he is due at least a few months of being injury free for AWs!