Fame does weird things to people. Maybe she felt flattered that this good-looking (debatable, but maybe true if your thing is a twitchy bag of bones wrapped in skin), famous, talented (again, debatable) was interested in her, a lowly runner.
Maybe he had buttered her up with some classic techniques like lots of eye contact, singling her out for praise or attention, learning her name out of all the runners (not a given in TV, especially amongst the talent).
Maybe she was self-conscious, carried self-doubt or low self-esteem. Maybe she'd had a recent breakup or suffered a loss that meant she craved attention.
Maybe he played the power game where he does something horrific, but then apologises and makes himself appear vulnerable and flawed. That kind of 'vulnerability', faux or not, can be intoxicating: see also all the women who believe they can change / save / help dickhead playboys.
There's also the culture at the time - don't forget women were being told it was ok to be promiscuous, to enjoy no strings sex, no such thing as 'slut v stud' anymore. When you are immersed in a culture that tells you it's all bantz, innit, it's hard to know where the line is, let alone when someone in a powerful position has crossed it.
I'm sure he popped it out with a cheeky smile on his face and asked her in such a way as it could be brushed off as a joke. So perhaps she's already unsure how to take him - it was just a joke, right? It wasn't creepy? He's just (openly) a funny sex pest, right? You know, when sex pest was almost a term of endearment. Everyone else thinks his jokes about chokey BJs are megalolz, right? So maybe I'm a prude?
I can completely understand being a young woman in an extremely male dominated, 'banter' laced industry and ending up in a situation where you find the attention of the 'hot' male star intoxicating.
It's kind of how predators predate.
We need to move away from the notion of rapists being angry, aggressive men in dark alleys and realise many of them are nice to their mums and top blokes to their friends.