Hey,
Yes you only need (and are restricted ) to upload a single file, it does not affect the results which is a binary pass or fail for the providers test run which should verify the api description, against the implementation.
You can combine your file output, into a single file and upload that, if you wish to be able to view it via the UI. We plan on having richer integration with specific verification tools, where the test information will be utilised in the rendered view of PactFlow.