I created a design with inputs and outputs, but no bidirectional ports. After fitting, the fitter report shows bidirectional I/Os for some signals that should be outputs only.
Check your fitter options. It is likely that "Pin Feedback" is enabled. This means that the software is allowed to use an output as a bidirectional signal in order to feed the output back into the device to be used by other logic (i.e., a bidirectional signal). If you do not want this, disable "Pin Feedback" in the fitter options and re-implement your design.