Hello! Note the frames in the export dialog are the exported frames, not the dopesheet frames, and so are based on the FPS in the export dialog. Eg, if your animation is 2 seconds long and you choose to export at 10 FPS, the frame range will be 0 to 19 (which is 2 seconds * 10 FPS = 20 frames, inclusive). The dopesheet is 30 FPS by default, so you can choose 30 FPS when exporting to have the export frame numbers match the dopesheet frame numbers. However, you may want to export at lower (eg for smaller export file size) or higher FPS (eg for a smoother exported animation).