Actually, Apple stopped "sandbagging" its guidance after Luca Maestri took over as CFO. Also, the consensus on the iPhone was 47 million, so 47.5 million was "in line," though some analysts guided higher. The consensus forecast for Q4 was $50.8 billion, so Apple's range of $49-$51 billion is slightly lower.
Apple already said that the Watch sales were greater than the increase in Other from last quarter because iPod and accessory sales declined. Luca Maestri told the AP that sales after 9 weeks were greater than the iPhone and iPad. We know that it took 74 days for the iPhone to hit 1 million, and the iPad sold 3.27 million in its first 89 days on the market. That suggests that Watch unit sales are probably close to expectations, but perhaps the mix is more toward the Sport than analysts were expecting. Apple is obscuring the data so we don't know for sure.