Maybe it's good advice to say "never make assumptions about ordering wrt hashes", but in this case the advice is misleading, because the form

%h = ( %h, foo => 2 );
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always* results in the hash %h containing foo => 2, regardless of what value (if any) $h{'foo'} had previously. Fletch's explanation is correct.

* That is, unless %h is tied to other behavior, e.g. altering or deleting keys or values according to some function.