Man pages were the Unix method of providing command-line documentation to a program. With GNU Info, see Info the usage of this method of documentation is highly discouraged. This is because Info provides a much more easier to navigate and read environment.
However, some operating systems require a man page for packages that are installed and some people are still used to this method of command-line help. So the programs in Gnuastro also have Man pages which are automatically generated from the outputs of --version and --help using the GNU help2man program. So if you run
$ man programname
You will be provided with a man page listing the options in the standard manner.