Not worried about the not bowing.  Even the article says that's not mandatory. And it's a good thing they know it, because Americans don't bow.  But the walking in front of the queen... that's something that heads of state shouldn't intentionally do, regardless of who is doing it or where they are.  The poor c  20d  horeography is probably the fault of the protocol officers from both sides, and what directly led to what I'm sure was the unintentionally crossed paths.