China Airlines CI004 TPE->SFO seemed to be considerably less full than CI003 SFO->TPE. The passengers on CI004 also appeared to have a higher percentage of non-Chinese-appearing people than on CI003. Lots of economy passengers on CI004 got economy class lay-flat seats (by being the only passenger in a block of 3 or 4 seats), and many others got to sit next to empty seats.

Perhaps it had to do with the choice of flight number (4 is considered an unlucky number among many Chinese people). But why would China Airlines choose 4 as a flight number, since they presumably know it is an unlucky number that results in negative marketing for that flight?