There doesn't seem to be any rational reason for such an attack. OTOH, there are reports such as the following -- in today's NY Times by Belgrade correspondent Carlotta Gall, in an article titled "The Chinese Mourn the Dead and Raise Questions": "One diplomat [nationality not identified] said NATO made the [Chinese] embassy a target on purpose, not least because such a mistake could have been so easily avoided. 'The American military attache was often coming to the embassy,' the diplomat said. 'They were surely some CIA people in the embassy here, and they had to have had the correct information.'"
Carl Remick