Yes, they should play it twice!!
I reckon that the examiner was probably a 'newbie' who hadn't examined any Grade 8s before, although that's no excuse for not reading the instructions properly - and very off-putting for the candidate involved.
Perhaps he was mixing it up with the bit that comes a sentence or two later, which says that a 2nd attempt may be allowed if necessary - for the actual singing back, not referring to the examiner's playing in the first place.