$results isn't a reference to an array, so you can't loop through it. According to the Net::Twitter documentation, it's a reference to a hash. This hash has a key "results", the value of which is an array ref, so you can loop through it.

You probably want something like...

foreach my $tweet ( @{$results->{results}} )
{
   printf(
      "%s <%s> %s\n",
      $tweet->{created_at},
      $tweet->{from_user},
      $tweet->{text},
   );
}
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