I found this as well, while writing test262 tests. Here's a code snippet showing how it's observable from JS:

class MyArray {
  constructor(...args) {
    console.log('called with', args);
  }
}
await Array.fromAsync.call(MyArray, {
  length: 2,
  0: 1,
  1: 2
});

This logs:

called with 
called with 2

I've opened #41 to fix this and added it to the May agenda for approval by committee.

My apologies for being absent from the discussion. This is a great catch, and #41 looks good to me.
@michaelficarra: I’ll get in touch on Element regarding next week’s plenary presentation.