Prove them wrong
The video had already spread around, and it looked like many in the room were already talking about it. The feat itself wasn't so impressive but the fact that a student of their age was able to do such a thing was. In the game, no abilities could be used, and some were even beginning to think the person in the video must have had some type of speed ability.
However, gaming systems usually had some countermeasure against abilities being used in this type of place and this was no exception. Due to the event not allowing the use of abilities, trackers and such were invented to see when MC cells were activated in a specific area. It was the same type of technology that was used in the watches.
Although the game couldn't stop the use of abilities, it could detect if someone was using it or not. The video had clearly come from someone who had full control of the video system that day. It would be silly for them to upload a fake video but not impossible.