You hit the exact point there. Because if a team loses a bunch of matches in the span of a month may not have an immediate effect on the ranking, but may affect the ranking in the future. Also doesn't FIFA's ranking take in count the U17 and U20 performances too? Argentina did better than Brazil in both of them, well not much of a difference in U17 but still.
NO. FIFA's ranking system uses ONLY the senior team's results at "Full A Level" & above games (ie friendlies, qualifications & championships - confederational, inter-confederational & World Cup Finals).