Baidu operates a large number of websites such as Baike, Zhidao, Wenku, and dozens more. Baidu tends to favor their own properties heavily in search results — it's not unusual for Baidu's websites occupy 50% of page 1 results for some queries.
This stretches across virtually every industry, topic, and category of search queries. This means for every site trying to get organic traffic in China, Baidu is not only dominant search engine but also the dominant competition.
This being the case explains why without exception, baidu.com will be shown as the #1 competitor in your ranking reports in Dragon Metrics — this is truly the highest ranking domain for all of your targeted keywords.