Tom,
Widening the gap in the collar is not a safety concern, so there is no reason for Festool to oppose the comment. However, I suspect that the actual corrective measure for your original problem was as you pointed out in the video---making sure the slot was at either the 9-O'clock or 3-O'clock positions. The closer it is to 12 or 6 O'clock, the less effective the clamping action would be.
Those are precision ground components, so I would not expect there to be tolerance issues requiring filing of the gap. Also, because that sleeve is hardened, I doubt that you filed even 0.001 from the edge. In all likelihood, your file simply opened the gap because it was not constrained inside the barrel. Once reinstalled back in the barrel, the gap was probably the same as it had always been.