I feel like because we know that Viaan isn't a bad guy per say, it is hard to categorize this whole event that took place between them. If this was something he'd done in the past to someone else and now to Katha again, then it would be a different case. We don't know for sure if he has made this offer to test others in the past but going by what's been implied in the show, let's assume this is his first time (obv not justifying this even for one time). Now you might say why Katha and not someone else? According to me, there may or may not have been a mild attraction (very unclear from the show) but more than that I personally think he was extremely intrigued by her ever since he met her. The first time he met her, despite her being late, he was quite impressed with her presentation and her perspective on the whole project which I think sparked a mild curiosity about her. Second, when Viaan found out about the fact that someone was leaking information to Pyramid, Katha had come in his room and there was this suspiciousness on his mind after he kind of sees her trembling making him further curious about her. Third, the fact that Katha went against him to persuade Amrita for the shipment on Dubai project impressed him even more. All these events combined had got Viaan thinking more about her and unconsciously he was already getting drawn towards her (again, I wouldn't call this attraction). But the moment he faces Katha's ask for 1 cr, his curiosity peaks and so he decides to test her which is why when she rejects his offer at first we see this relief on his face. But when Katha comes back to accept it, he looses his shit as he gets triggered by his past trauma.
Now that's what I feel about the actual offer. As for why he went on to doing the deed, I think because he was really expecting her to not show up at all at the hotel, he loses his shit for the second time when she shows up. The same curiosity he had for her awakens again when she shows up so he finally decides to go for it as a second test but eventually gets drawn into her when she says that she wasn't there to back out (this may or may not make sense to everyone). For Katha, the act itself didn't mean much because her main motive was the money. But for Viaan, he was left with disappointment when he saw her leave with the money at the end of the night because she couldn't prove wrong his perception about woman which is what he wanted her to do.
Keeping all that in mind, I don't believe that a single term can be used to describe this whole situation. Viaan didn't know about Katha's situation and Katha didn't know about Viaan's past. Both were unable to read each other leading this whole situation to take place. Viaan is responsible for his actions while Katha is responsible for hers. Only thing is, Viaan's weight of wrong actions are higher than Katha's as he initiated it while Katha had valid reasons for doing it.