The export cost in the above proposition refers to China's export cost expressed in foreign exchange (foreign currency), and certainly does not refer to other countries.
Two examples upstairs show that the cost expressed in RMB remains unchanged, but the cost expressed in US dollars (which is the usual way to collect foreign exchange from exports) has increased. For example, China exported a suit 6.85 yuan/USD 1 year ago, and the export breakeven price was 100 USD, so it can be converted into 685 yuan (export cost), but now the appreciation of RMB 6.65 yuan can be converted into 1 USD, and the export breakeven price of this suit is about/kloc-0.
To be exact, the appreciation of RMB leads to the increase of foreign exchange price of China's export commodities, which weakens the price competitiveness of China's export commodities.