If he believes that, then he just announced that he wasted millions of dollars of donor money to build a useless building.
He recalled visiting the PLO headquarters in Jerusalem in 1964, saying that just as it was the headquarters of the PLO then, so it will return.
For some reason, he didn't mention that the PLO in 1964 had explicitly rejected the idea of a Palestinian Arab state on the West Bank, saying that they have no ambitions to take away Jordanian territory. From its original charter:
Article 24: This Organization does not exercise any territorial sovereignty over the West Bank in the Hashemite Kingdom of Jordan, on the Gaza Strip or in the Himmah Area. Its activities will be on the national popular level in the liberational, organizational, political and financial fields.
Also in 1964, the PLO's goal was not to build a state - it was only to destroy Israel. Nowhere in its charter does it use the word "state" or "nation" in terms of its goals; it only talks about a "homeland" and the "liberation of Palestine" that is strongly implied - along with the concept of a Palestinian Arab people - to be a tactical move on the way to pan-Arab unity:
Article 11: The Palestinian people firmly believe in Arab unity, and in order to play its role in realizing this goal, it must, at this stage of its struggle, preserve its Palestinian personality and all its constituents. It must strengthen the consciousness of its existence and stance and stand against any attempt or plan that may weaken or disintegrate its personality.
Article 12: Arab unity and the liberation of Palestine are two complementary goals; each prepares for the attainment of the other. Arab unity leads to the liberation of Palestine, and the liberation of Palestine leads to Arab unity. Working for both must go side by side.
The only nation it speaks about is the negation of a Jewish nation, anywhere:
Article 18: The Balfour Declaration, the Palestine Mandate System, and all that has been based on them are considered null and void. The claims of historic and spiritual ties between Jews and Palestine are not in agreement with the facts of history or with the true basis of sound statehood. Judaism, because it is a divine religion, is not a nationality with independent existence. Furthermore, the Jews are not one people with an independent personality because they are citizens to their states.Within the same document we see the attempt to artificially create a people who nobody had heard of a few decades earlier, and to deny the nationhood of a people who had been identified as such for millennia.
This was the PLO of 1964 that Abbas nostalgically recalls. And this document is still available on the PLO's UN website.
And while its stated goals might have changed, its actions are still remarkably consistent with the actions of today's "moderate" Mahmoud Abbas.