CGI versions before 5.00 for Perl take request parameters from the process command line arguments for an unrecognised REQUEST_METHOD. For a REQUEST_METHOD such as OPTIONS, CGI falls through to its offline debugging mode, which is on by default, and builds the parameters and path_info from the process's command line arguments.
https://metacpan.org/release/LEEJO/CGI-5.00/changes
https://metacpan.org/release/LEEJO/CGI-4.72/source/lib/CGI.pm
https://github.com/leejo/CGI.pm/commit/b753ff75a3bc4554c075cc37c1db605a55297029.patch