Looks like after, due to being lower than the average analyst expectations... had been predicting $37b revenue, vs. actual report of $35b.
They also missed the EPS by a dollar ($9.32 vs $10.35)
They missed the analysts predicted revenue and EPS, but not their own guidance: revenue of $34 billion and earnings per diluted share of $8.68. Wall Street investors go bullish when iPhone sales slow, and bearish when sales are exploding.
this is traditional: they almost always undershoot the over-expectations
The drop came after the results were reported.
A move like that, especially after hours, is almost always news (earnings in this case) related.