You're passing strings ($dates, $quan) instead of arrays (@dates, @quan) to the constructor:

Replace

my $dates = "20070410, 20070415, 20070417, 20070418";
my $quan  = "10, 20, 15, 42";
my $table = new Data::Table( [ [$dates], [$quan] ], [ 'Dates', 'Values
+' ], 1 );
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with

my @dates = (20070410, 20070415, 20070417, 20070418);
my @quan  = (10, 20, 15, 42);
my $table = new Data::Table( [ [@dates], [@quan] ], [ 'Dates', 'Values
+' ], 1 );
[download]

and it should work (tested).