Possible shark sighting in Réunion

Late afternoon surf session, there were just 3 guys out including myself.
Water was clear, sun was low in the horizon and the wind wasn't too strong.
While waiting for the set, I submerged my camera to see later what's the bottom looks like, and did a 360º panorama. After that, continued surfing for 40 minutes until the sun finally set.
But when reviewing the video at home, I noticed we were not alone…