百 ('hundred') is figurative — 'the many Yue tribes.' Han-dynasty texts grouped these peoples together because they all called themselves Yue (
越) but were actually dozens of distinct groups:
于越 in Zhejiang,
闽越 in Fujian,
南越 in Guangdong,
骆越 in Vietnam. Modern Vietnamese 'Việt' descends from the same word.