If there was an agreement not to form a unity government, there would have been no reason to keep it secret. On the contrary, the PA would have gotten its money from Netanyahu while depriving him of an excuse to hold on to it. (The US renewed aid to the PA already.) Besides, with MA not far away, everybody would have realized that such an agreement was part of the deal. In any case, not forming an interim government is a bad idea, there would be no confidence that the losing party would yield control of its territory. This is just a false report, as many are.
Hamas' Khaled Meshal met with Saeb Erekat in Qatar (Haaretz)
from the article: Hamas: Palestinians won't form interim government before elections