It's actually correct. You are talking about a group of people. It's then referred to in the singular. If you say that only 1 out of 3, or only some people, you would then say are.
Pixie: " If you say that 'only 1 out of 3…people', you would then say 'are.'" No, Pixie, no. You are making the mistake most Americans make, namely, that the verb simply agrees with the noun immediately preceding the verb. Only ONE out of three people IS…"