[chef] Question on Deep Merge Documentation

[< >]

I was reviewing
http://docs.opscode.com/essentials_node_object_deep_merge.html#substitution ;
and
I got thrown for a loop with this example:

For substituting an array with a hash:

role_or_environment 1 [ "1", "2", "3" ]
+
role_or_environment 2 { :x => "1" , :y => "2" }
=
{ :x => "1", :y => "3" }

I'm unclear why :y would be "3" and not "2" in this example. Is this a
documentation error, or am I just misunderstanding something?