Actually, it does not say to use at least 32 GB; it says exactly the opposite.
The HP recovery manager software is not compatible with many USB storage devices larger than 32GB. HP Recovery Manager displays the total size of the source files when going through the creation process. You can stop at this screen during the creation process to know what size of storage device you should use. Use a storage device that is larger than the size of the source files, but not larger than 32GB.