Looks as though it's Robert Murat who has the scar not David Payne.
How on earth could Yvonne Martin think that David Payne could be the person carrying a child, he has receding hair and glasses!!
IMO YM saw both Murat & Payne that morning at different times & got confused when recalling her first meeting with Kate.
In "madeleine" Kate described her meeting with YM & DP was certainly the person who ushered her away. Kate also wrote "This woman would pop up several times in the days & months to come & I still don't really know who she is or what she was trying to achieve".
In the very next paragraph, Kate referred to Stephen Carpenter returning with Murat, who had offered to translate, which fits the timing of both YM & RM.
http://www.mccannpjfiles.co.uk/PJ/ROBERT-MURAT.htmsnipped
On Friday, 04/05, woke around 09:00, took a bath, went to the kitchen to his mother, the latter told him that something terrible had happened, because a child had disappeared in Praia da Luz, according to 'Sky News' that she had been watching. At once the respondent and his Mother went to look in the garden, walled with a fence of 1m in height, checking if the child had managed to enter, which in a way was almost impossible without aid. In one corner of the garden is a greenhouse, which was searched, and then they saw an English passer-by on the outside, he does not know the identity. When asked about this, he was told that the child had disappeared. Accompanied by that person, he went to the place of the disappearance, and was introduced to the parents of the child, as he spoke the two languages, Portuguese and English.