Part of why Cook perhaps felt compelled to weigh in: worries of a China-led global economic slowdown have kicked into high gear, with U.S. stocks also bruised. These fears have hit firms with great exposure to the China market especially hard. Apple’s shares have slid some 23% over the past month.

“As you know we don’t give mid-quarter updates and we rarely comment on moves in Apple stock,” Cook wrote in an e-mail Monday morning to CNBC host Jim Cramer.

But Cook went on to sound practically bullish about the market’s recent performance. He said Apple’s growth remained “strong” through July and August, with growth of iPhone activations accelerating in recent weeks. The App Store has also posted record growth the past two weeks, he said. Cook went on to tout the potential of the market, especially with the expanding middle class in China.

China is a particularly important market for Apple, with sales growth in that region outperforming the overall company’s performance. For the latest fiscal year, Greater China sales totaled $29.85 billion, up 135% from just three years earlier. The Greater China segment includes China, Hong Kong, and Taiwan.

Apple has successfully outmaneuvered competitors in the market. Unit growth for iPhones surged 87% in the most recent fiscal quarter, while research firms have estimated the smartphone market expanded by only 5%. That means Apple has been easily stealing market share. Revenue has also been boosted by strong Mac sales and revenue from the company’s App Store.