From the rather sketchy Daily Mail story the two witnesses did not witness anything taking place. The woman herself tried to withdraw the charge even before the CCTV footage was shown. It seems more a case of the police trying to tamper with the evidence. In the US or UK witness hearsay alone with the plaintiff withdrawing the claim (hence what she told them) would not require CCTV evidence. This is because the case would not even go ahead and waste the court's time.
If your friend shows up back at the bar after having 'gone for a walk on the beach' with some guy, obviously drunk, with an injured wrist and more injuries on her back, confused, and knowing there was sexual contact, it seems that it would be very natural to believe that your friend was raped and to urge the friend to go to the police and to go with your friend to the police.
Many rape victims withdraw their complaint or attempt to do so because they don't want to go through all of the ugliness that an investigation and trial will involve, in addition to dealing with the trauma of the rape. Which would explain why the police insisted on moving forward with charges in the face of the victim's withdrawal of complaint. What is not known is if this incident was an isolated incident, or if there has been a rash of sexual assaults or if the accused man has been a suspect in other assaults. We have zero idea, but if any of these were going on, it would make sense that the police would want to proceed with charges.
The employer, oh, so helpfully had video that the sex was consensual. It did not have any BAC evidence. We have no idea if she was too drunk to consent by US standards or by the standards of Cambodia. It isn't just US college campuses that regard 'too drunk to consent' sex as rape. But not all countries have the same laws.