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.