Connections does not use a custom post type, its uses a custom db schema. Two reasons really, but only one is important. Connections is older than custom post types. I have considered migrating the data and may still at some point in a future version, maybe. Or may not because the current db schema is more fitting for directories whereas custom post types is better suited for, well, posts and other types than fit well within that schema.
If I may, why do you ask?