I know who they are quoting. I also re-listened to what he said because at the time I'd made the same assumption.

Apple execs are infamously careful about how they word things. Federighi could have said they won't allow other operating systems, but he didn't because that's not what they did or were planning.

If they didn't intend for this to be possible, they wouldn't have shipped it this way and documented how to do it.