Unless specific qualifiers are added, i.e. "Cross Brazilia at FL370, then descend and maintain FL360.", then an altitude assignment is in force until amended. It is completely normal to have a situation where your altitude assignment is planned, and expected, to change later in the flight. The flight, however, DOES NOT change altitude until told by ATC to do so.
If they had a flight plan that predicted a descent to FL360 after Brasilia, shouldn't they seek contact with ATC to ask for clearance ?
(This is just a question ... I am not sure what the right answer would be)