That's a very confusing example because it looks like an object but isn't. That example would still work if you remove the OO looking stuff:

#!/usr/local/bin/perl
use strict;

my $dave = subref("dave", "oranges", "grapefruit");
$dave->("debug message");

sub subref {
        my (@stuff) = @_;
        return sub { doit(@stuff, @_) }; # <-- closure here?
}

sub doit {
        print shift, ": ", join(",", @_), "\n";
}
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Yes, it is a closure, but it's also an anonymous sub ref, so it's showing multiple things. Here's a much simpler closure:

my $foo;

sub bar {
    $foo++;
}
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After execution, bar() has a private copy of $foo. TheDamian uses this in his book to do private variables for classes.