It's not the parenthesis that create the list. They just group things. It's the comma. See:

#!/usr/bin/perl -w

use Data::Dumper;

my $sort_func    = sub { $b <=> $a };
my @to_be_sorted = (1,2,3);

# sort LIST
my @new = sort ($sort_func, @to_be_sorted);
print Dumper \@new;

# sort LIST
@new = sort $sort_func, @to_be_sorted;
print Dumper \@new;

# sort SUB LIST
@new = sort ($sort_func @to_be_sorted);
print Dumper \@new;
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