He is but he looked even in Sao Paulo to be slower, worn out and his groundies looked unusually weak.
Nadal has been at the top of the game since he was 18, he reached #2 just after turning 19- his body has taken years of battles. It's understandable if he declines at 27.
he did look slower and more worn out but pretty impossible to read anything from it when considering he was gone from the game for so long and may be just 'playing it safe' with the knees, i.e. not trying as hard to be super careful