Answer: We have assumed constant returns to scale.
Explanation:
Comparative advantage simply stated that an economy should produce the goods whereby the said economy has a lower opportunity cost than its counterpart.
Based on the analysis in the question, the inaccurate assumption is that we have assumed constant returns to scale. This means that an increase in the inputs such as capital and labour which are used in producction will also cause an identical increase in output. In reality, this isn't always true.