The man pages state that:
-perm -mode means that all of the permission bits in mode are set for the file.
-perm /mode means that any of the permission bits in mode are set for the file.
When I created two directories in /tmp with permissions 1777 and 1755, and used these commands, both directories were found with both 1777 and 1755 permissions.
find / -perm -1000 -type d
find / -perm /1000 -type d
This is why I'm confused. I'm using CentOS 7 as my distribution.