There is a filtering pass on the raw coordinates to remove the high frequency noise produced by the digitization. There is more information about the exact process and the cutoff frequency selected in the about tab of the data analysis dialog.
The approach comes from sport science literature, I don't know its relevance to burst swim of fishes. But I think it should still be better than the raw coordinates.
The spreadsheet export from the main menu does not have the filtering, it's just the raw data. The shift by 4 frames is strange. Maybe one of those files where the first image has a time coordinate different than zero and cause some issues.
