Both commands have the same inode number, so they consist of the same code.
$ ls -il /bin/{link,ln}
1152921500312524105 -rwxr-xr-x 2 root wheel 101968 Mar 21 07:13 /bin/link*
1152921500312524105 -rwxr-xr-x 2 root wheel 101968 Mar 21 07:13 /bin/ln*
If you run man link, you get the same man page as for ln. The difference is that link doesn’t take any options and always creates a hard link.
SYNOPSIS
ln [-L | -P | -s [-F]] [-f | -iw] [-hnv] source_file [target_file]
ln [-L | -P | -s [-F]] [-f | -iw] [-hnv] source_file ... target_dir
link source_file target_file
...
When the utility is called as link, exactly two arguments must be supplied, neither of
which may specify a directory. No options may be supplied in this simple mode of operation,
which performs a link(2) operation using the two passed arguments.
Honestly, I don’t see a practical use for link (I didn’t even know this variant exists, and I’m using Unix-style systems for >30 years now).