He knows that she is up to something. He also knows that she can somehow figure out malintent. It was a test. He might be interested in her, but still perceives her as a threat.
Yes I agree with @geshra and I think a couple others mentioned about the importance of testing her. I at first thought he wanted to off her since he still views humans as useful or ones to kill and feel better. Since his interest/like isn’t that high I thought his patience was at its end. Then I thought if she had went ahead and began to drink the tea not knowing something may be wrong with it, he could stop her and think that maybe her detection skills are limited. Since she was taking so long and avoiding drinking the tea it may have made it more obvious that she can detect murderous/malicious intent.
Was the tea legit poisoned? Like the ending I couldn’t tell I just thought it was supposed to represent how scary that situation but if he tried to poison her that was kinda silly?? He’s been interested in her and what her deal is, and is cautious if she’s the chosen one? Or something that if he kills will bring him to his end so that was so risky??