Why an alternate fleet's allegiance matters as much as its size

What happens if similarly sized People's Republic and Republic of China fleets from another dimension replace the present Chinese navy?

The immediate response would be to establish what had happened; whether the arriving fleets fought would depend on their relationship in their original setting.

The scenario supplies fleet size but leaves political relationships undefined. The first practical problem is identifying the newly arrived forces and understanding the event. Equal or comparable strength alone does not establish how those fleets would behave. Conflict between them is treated as conditional on the views and relationships they bring from the alternate setting.