TLDR;

When restructuring defaulted bonds, Argentina agree to borrow in US dollars. They further agreed:

- to pay all bond holders equally.

- to be governed by New York state law.

- to NOT include a collective action clause in the bond agreement which would have forced minority recalcitrant bondholders to enter a restructuring agreement, if a super majority of the bondholders agreed.

A small minority (2.5-3%) refused to accept the 70-75% haircut the Argentina government was forcing on the bondholders (fyi: previously the largest haircut in sovereign debt was 30%)

(from one of the dealbook article's comments)