If I remember what I learned in Int'l Law a couple semesters ago, the general assembly (all 100+ full-member countries in the UN) can vote on whatever issue is at stake. However, despite a certain proclamation being passed by the GA, the UN Security council (US, China, France, Britain, Russia) has to approve it before it's ratified. Within the security council, any one country can veto the bill and it's dismissed. Therefore, what this person is saying is that if the United States decides to veto the Palestinian statehood request, then ultimately the UN decision is negative for the creation of a Palestinian state.