Perhaps you could post a screen grab so we can see what you’re describing. Are you sure your exported wave files really are mono? What does it say about the files in the media pool?
If you have stereo files (which you have, if the files show 2 channels), then the batch export was not mono.
The batch export format does not depend on what format the files were originally recorded at, just as the file format does not depend on the kind of track (mono / stereo 5.1) it is imported to.
Anyway you could split the files on import…