I don't consider it in terms of ranking, he was a couple times ranked much more lower but every time after an injury and losing of previous year's points.
He has lost six consecutive tournament matches. Admittedly he had a similar streak two years ago but after that was the best at the South American swing. Now, with defeats to Mayer and Nishikori (well, Top 20 player but playing first ATP event in South America) his confidence must be really low, and it's tough to expect he will go far in Acapulco where the draw is even more demanding than in Sao Paulo and Buenos Aires.
Now that Davis Cup awards ranking points you can't exclude his win. Every year is different. Just because he had a great South American run two years ago doesn't mean it's always his strongest part of the season. In fact traditionally it was one of his weaker months.
Losing to Mayer and Nishikori is nothing compared to losses he's had in the European clay swing to much lower ranked players. The only real suspicion here is that he's 32 years old when critics always question motivation. Every losing streak is hyped ten fold because of age.