@Snickrot See, I don't really have a problem if that was it, but with the way that it's portrayed in the manga at least it
feels like this is brought on entirely due to him giving her the item (and maybe her knowing that he's not a horrible person from before), but the way that the conversation was about the cup, he didn't find it odd, and how she jumped straight to being his slave and offering to die to protect him instead of trying to seduce him or something it just feels odd to me.
Honestly, several of the interactions with her have seemed a bit weird to me, like her seeming to be overly suspicious of him in their first encounter (though that's easy enough to believe that we lacked the full context to), but I'll see how things go. If anyone who's read the source material can chime in if the manga is cutting out some content that'd be appreciated because this chapter at least felt like we were missing a good 75% of the conversation to me.