Exporting anim curves uses the copyKey MEL command to copy the keys to the API clipboard and then exports the clipboard contents to the anim file. The entire operation is contained in the file export.
The File > Export Selection options window lets you set the same options as Edit > Keys > Copy Keys which are used to export the animation from the selected object(s).
When an anim file is exported, any information previously on the API clipboard is replaced with the new anim curves after the file export.