Methinks that is a typo as Boeing no longer builds the 737-300, only 737-600, -700, -800, and -900.
I couldn't locate anything on Boeing's site so maybe the deal isn't finalized yet.
You were proven to be correct:
China Eastern Airlines to purchase 6 Boeing airplanes
China Eastern Airlines Corp. announced here recently that it would buy six 737-700 airplanes from US aircraft maker Boeing Co. -- another big deal for the company after it agreed to buy 20 A330-300 aircraft from Airbus inOctober.
The six planes, worth 2 billion yuan (about 241.5 million US dollars), which will be delivered starting in January 2006, will be used for both international and domestic routes, according to the contract signed between China Eastern Airlines and Boeing lastweek.
Currently, there are 42 Boeing airplanes operational in the fleet of China Eastern Airlines, including 737-300, 737-700 and 737-800 jets, said the company.
By the end of 2005, 13 more Boeing airplanes will be deliveredto China Eastern Airlines, increasing its number of Boeing jets to55, said the state-owned airline.
Source: Xinhua
http://english.people.com.cn/200412/28/eng20041228_168875.html