“the seventh month.” The fact that the Jews were celebrating the Feast of Tabernacles in the seventh month shows that at that time they were using a Nisan-based calendar like the Babylonians.
“the children of Israel were in the cities.” The Judeans who returned to Judah mostly returned to their ancestral homes in the various towns of Judah.
“as one man.” This is an idiom meaning that the people were unified.