Why might intra-industry trade seem surprising

from the point of view of comparative advantage?

Intra-industry trade is the exchange of alike products belonging to the same industry.

Comparative advantage is the ability to produce a good or service at a relatively lower opportunity cost than others.

In the comparative advantage principle, the nations which trade with each other for gains should be differently skilled but in Intra-industry trade, the trade occurred between the countries that have identical types of resources.
According to comparative advantage, it wouldn't make sense for a country to import a good it exporting, however, because of competition, diversity of products, and quality preferences, intra-industry trade occurs.
Example: Many countries manufacture cars, so why would countries that are efficient car makers import cars from other countries? To have a higher diversity of products and qualities.
Comparative advantage works in a one-dimensional scenario, where exchanged goods are identical.