If the recent sell-off of Apple (NASDAQ:AAPL) stock wasn't ridiculous enough in its own right, what is even more baffling is one of the alleged key reasons for the weakness. It all began when, earlier this month, The Wall Street Journal ran the doom and gloom headline, "Devalued Yuan Set to Take Bite Out of Apple, Give Boost to Chinese Rivals." But a closer look at all this nonsense reveals why investors will probably eventually look back at this period as an irrational moment and an excellent buying opportunity.

Apple Store China

Reviewing Apple's best market
Apple's Americas geographic segment is no longer its best. Yes, it is still the company's biggest market. At $20.2 billion in revenue during the company's most recent quarter, it represents about 40% of total revenue. But it's another geographic segment that is driving the majority of Apple's underlying growth: Greater China. As the company's second-biggest and fastest-growing segment, this is the market investors should be excited about.

Growth in Apple's Greater China segment is astounding. During the fiscal third quarter, Greater China revenue was up 112% year-over-year. To really drive home how well Apple is doing in this region, consider that overall smartphone sales in the region were up only 5% for the period.

After China, Apple's next best geographic segment in terms of growth was its "Rest of Asia Pacific" segment, which grew 26% year-over-year. Its Europe market came in third, up 19% from the year-ago quarter. Americas revenue was up 15% during the same period, and Japan was up 9%.

If struggles in China really do eventually hurt the company, the impact probably wouldn't come close to taking "a bite out of Apple." The worst-case scenario is probably one in which Apple's growth in the region could decelerate. But even if Apple's growth in China was halved, the region would still be growing the fastest.

As it turns out, however, China struggles don't seem to be affecting Apple at all.

Tim Cook speaks up
Apple CEO Tim Cook, in a letter to CNBC's Mad Money TV host and investor Jim Cramer, insisted all is well with Apple in China. Even more, Cook suggested Apple is actually doing great in the market.

Tim Cook Oct

CEO Tim Cook. Source: Apple

Here's a copy of Cook's letter to Cramer: 

As you know, we don't give mid-quarter updates and we rarely comment on moves in Apple stock. But I know your question is on the minds of many investors.

I get updates on our performance in China every day, including this morning, and I can tell you that we have continued to experience strong growth for our business in China through July and August. Growth in iPhone activations has actually accelerated over the past few weeks, and we have had the best performance of the year for the App Store in China during the last 2 weeks.

Obviously I can't predict the future, but our performance so far this quarter is reassuring. Additionally, I continue to believe that China represents an unprecedented opportunity over the long term as LTE penetration is very low and most importantly the growth of the middle class over the next several years will be huge.

Cook's reference to "an unprecedented opportunity over the long term as LTE penetration is very low," is worth emphasizing. Consider the world's wireless carrier, China Mobile. China Mobile has about 819 million wireless subscribers and just 209 million are 4G customers. And the rate of subscribers switching from 3G to 4G is incredible -- just six months ago, China Mobile's 4G customers numbered just 107 million.

As I've insisted several times in the past few weeks, this sell-off is presenting an excellent buying opportunity in Apple stock.

Daniel Sparks owns shares of Apple. The Motley Fool owns and recommends Apple. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.