Load a panels display in code
The relationship between tables and their exported datasets is declared via the export key in a table's schema definition. We can see that key both for page_manager_pages and panels_display. 

ctools also allows the definition of a default hook. If non was provided it will fall back to default_{table}. 

When loading a ctools exportable via ctools_export_load_object() ctools will first query the table for objects, then invoke the default hook to retrieve any objects stored in code.

When page manager pages are exported, panels_display objects are not declared separately under their own hook, but are wrapped in hook_default_page_manager_pages().
In order to retrieve them by their UUID they would have to be declared within hook_default_panels_display().