I presume he was reacting to:

if (@ARGV)
{
  if (@ARGV == 1)
  {
    Download($ARGV[0]);
    EXIT(0, 'SUCCESS. Argument was received from command line.');
  }
  else
  {
    PrintUsage();
    EXIT(-1, 'Argument missing.');
  }
}
else
{
  Download(GetArgs());
  EXIT(0, 'SUCCESS. Argument was received from stdin.');
}
[download]

That can be rewritten as:

if (@ARGV) {
    if (@ARGV == 1) {
        Download($ARGV[0]);
        EXIT(0, 'SUCCESS. Argument was received from command line.');
    }
    
    PrintUsage();
    EXIT(-1, 'Argument missing.');
}

Download(GetArgs());
EXIT(0, 'SUCCESS. Argument was received from stdin.');
[download]

which reduces the number of lines of code and makes the logic clearer. Even better would be:

use strict;
use warnings;

if (!@ARGV) {
    Download(GetArgs());
    EXIT(0, 'SUCCESS. Argument was received from stdin.');
}

if (@ARGV == 1) {
    Download($ARGV[0]);
    EXIT(0, 'SUCCESS. Argument was received from command line.');
}

PrintUsage();
EXIT(-1, 'Argument missing.');
[download]

which avoids nested code paths altogether. Wherever the code path can't continue out of a previous block there is no need for an else. That avoids nesting following code and generally makes the logic easier to follow.