This was also my first thought, but now playing with it I don't understand how the following makes sense:

<?php
function g() {
    yield '1' => 'one';
    yield '0' => 'zero';
}

function test(...$z) {
    var_dump($z);
}

test(...['1'=>'one','0'=>'zero']);
test(...g());

Yields:

array(2) {
  [0]=>
  string(3) "one"
  [1]=>
  string(4) "zero"
}
array(2) {
  [0]=>
  string(3) "one"
  [1]=>
  string(4) "zero"
}

So in both calls, the item with key '1' gets assigned to array index 0...
I see it is consistent between arrays and generators though, I just don't understand how this would make sense.
This question came to me after seeing the test which generates keys 100 until 102 but ends up with lower array indices