Vince Lia couldn't play for NZ because he'd already played for Australia in an Official Competition, and wasn't eligible for NZ at the time.
Andrew Durante never played for Australia.
Marco was eligible to play for Chile until he played for us in an official competition.
Until Fitzgerald plays for NZ in an official competition match, he can switch allegiances.
You have to have held the other nationality at the time you played for the other country for a friendly to be able to change. Because Durante never played for Australia in that friendly, he thus was deemed never to have played international football (for anyone) so when he played his 1st international friendly, he had dual nationality and was not tied to Australia. If subsequent to Durante playing for us (for example) in a friendly only, he would still have been able to switch to Australia. Fitzgerald didn't have the option of choosing another nation like Marco thus, to make the switch to another nationality (Japan) he can't have ever had taken the field for NZ because at the time of that game for NZ, he was not eligible for Japan regardless if it was an official game or not. To be able to change nationalities, you much have had another one at the time you played in any international game (although competition games tie you to that country)
Article 17 Acquisition of a new nationality
Any Player who ... [assumes] a new nationality and who has not played international football [in a match ... in an official competition of any category or any type of football for one Association] shall be eligible to play for the new representative team only if he fulfills one of the following conditions:
(a) He was born on the territory of the relevant Association;
(b) His biological mother or biological father was born on the territory of the relevant Association;
(c) His grandmother or grandfather was born on the territory of the relevant Association;
(d) He has lived continuously for at least five years after reaching the age of 18 on the territory of the relevant Association.
He has played for NZ so the rest is irrelevant.