Did you want [ '1 2 3 4' ] (one element array!?), or [ 1, 2, 3, 4 ]? Fix:

use Data::Diver qw( DiveRef );

my $data = {};

while (<DATA>) {
   chomp;
   my @keys = split /:/;
   my $val = pop(@keys);
   my $ref = DiveRef( $data, map \$_, @keys );
   $$ref = [ split ' ', $val ];
}
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