Instagram's four different post types, and why they behave differently
A single-video feed post, a carousel, a Reel and a Story are four distinct objects behind the scenes. Feed videos are usually capped near 1080p with a moderate bitrate; Reels are handled by a separate pipeline with its own compression; carousels bundle several media items that each need extracting on their own; Stories expire after twenty-four hours and vanish entirely.
Grabnode reads the post type from the URL and returns everything the post contains — for a carousel, that means each video and each photo listed separately rather than only the first slide.