China is not India! the penetration rate of smart phone and computer are much much higher than your imagination! Even in the poorest area, peoples are easy to obtain computer or smart phone. Because of there are many Chinese vendor provide very cheaper smart phone and computer. Entire China are fully covered by Internet and Cell phone signal at least 10 years ago.
From your writing, I guess you are a Chinese living in the cities? Probably quite well off too. I believe you are applying what you see in the cities to rural areas. You are correct in saying computers and smartphone penetration is around 60% in China and I have no doubt mobile internet covers most parts of China too. However, mobile internet is expensive for rural Chinese relative to their annual income.
I did not plug the 30% figure out of thin air. It is not my imagination. Mobile internet subscription is around 800 million early 2014, total population is around 1.3 billion. You have to take expats, one person owning multiple mobile numbers, and rural businesses into account. Actual Chinese individuals, having mobile internet bitcoin ready devices, out of total population should be less than your estimate. My 30% could not be far off.