Can an unbeliever afflict others with the the evil eye?

Yes, affliction by the evil eye can indeed come from a disbeliever. The proof for this is Allah’s saying: (And indeed, those who disbelieved would almost make you slip with their eyes when they hear the message) [Al-Qalam/51].

Al-Suddi said: "They would afflict you with their eyes."

This is also indicated by the general statement of the Prophet, peace and blessings be upon him: (The evil eye is real).