Not surprising in the least imo. I think he's saying he respects Sentomaru for sticking true to his duty to Vegapunk.
It's right on brand for Kizaru. Doesn't seem like he's wavering at all, he's doing what needs to be done for the W.
What surprised me more is Saturn's respect for Kizaru's friendship, even Saturn was softer than Kizaru here, he was legit pulling at his hairs and couldn't even order Kizaru to simply take his buddy out. Kizaru said fuck all that Sentomaru needs to be dealt with.