I agree with this approach.

It gives him the awareness that you have noticed, when he may not realize it himself. I know, for me, sometimes, I don't realize where my eyes are exactly. Especially when I am listening intently to something that is slightly uncomfortable to me.

It also gives him the chance to explain, and open a discussion. Why he is doing it, if it is intentional, and also why it is creepy to you. If this is the only thing about him that feels off for you, it may be something that can be worked out.

I think giving him the awareness that you are aware may be enough for him to check his behavior. Even if he is not entirely aware, he may pay more attention after asking about it.