1)
Why did they mention Nebuchadnetzar's arrival?
1.
Rashi: We were forced to come to the city. Therefore, now we live in houses.
2.
Malbim: Since there is danger [and Yonadav intended that we live long], also in this we obeyed his command!
2)
What is the meaning of "Bo'u"?
1.
Radak: It is an expression of being zealous, like "Lechu v'Nelchah ha'Gilgal" (Shmuel I, 11:14).