How are hash keys sorted

Until today, I thought that hash keys were randomised when returned. However, the entry in perldoc on keys suggests otherwise:

Hash entries are returned in an apparently random order. The actual random order is specific to a given hash; the exact same series of operations on two hashes may result in a different order for each hash.

There are other entries on SO that relate to this - most pertinent is the accepted answer to this question.

The following code returns apparently randomised hash keys:

 my %hash;
    $hash{$_}++ for 1 .. 100; 

    say for keys %hash;

Can anyone help me understand how this is not actually random?