The disk head got stuck because the head was ‘glued’ to the platter by stiction (https://arstechnica.com/civis/viewtopic.php?t=1051141, https://hardrecoveryman.wordpress.com/2012/10/26/release-of-...; a fairly common issue in the day for certain brands of hard disk, and he did a quick and dirty ‘repair’, first by trying to get it unstuck through inertia, then by opening the enclosure and forcing the head to get unstuck.
He likely did not use a clean room, so that repair probably was temporary.
> and then started looking through its contents by dumping it to the screen (sorta like if you look at a raw hex dump from dd or a tool like Spinrite)
They ‘just’ booted the disk and used the ProDOS CATALOG command (or its shorthand CAT) to list the files on the disk.