The equivalent print would have been print "@k{qw(A B C)}";. Remember that m/.../ is a quote-like operator. The element seperator for interpolated slices and arrays is the value of $".

#!perl -l

my %k;
$k{'A'} = 'Foo';
$k{'B'} = 'Bar';
$k{'C'} = 'Baz';

{
   # What goes for double-quotes...
   print "@k{qw(A B C)}";    # Foo Bar Baz
   local $" = '';
   print "@k{qw(A B C)}";    # FooBarBaz
}

{
   # ...also goes for the regexp operators.
   print qr/@k{qw(A B C)}/;    # Foo Bar Baz
   local $" = '';
   print qr/@k{qw(A B C)}/;    # FooBarBaz
}
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Update: Added qr/.../ to the example.