You can judge for yourself if he was embellishing or not. Looks to me like a slight embellishment. Honestly, I don't think this is something worthy of taking down Bill O'Reilly.
UPDATE: I just found this tweet from Bruce Wolf, who disagrees with me.
I'm conservative, and I don't like NBC standards being higher than Fox's. "Many people killed"? That's truthiness. @HowardKurtz
— Bruce Wolf (@BruceWolfChi) February 24, 2015
Another UPDATE: The Washington Post examines the charges here. I think the conclusions in this article are exactly correct. He is essentially guilty as charged of embellishing, and it absolutely does not matter to his bosses.