Depending on the equipment chosen before the race starts, the performance of each boat can be different in equal weather conditions. It is possible that your competitor may have equipped his boat differently, and that it will be faster under the same weather conditions.
However, the position of your competitor as you see it on your game screen may be a few minutes old. Your boat's data is displayed in real time, but other boats' data is refreshed less often. This makes it possible to reduce the flow of data transmitted on the game, and to offer you faster and more fluid gameplay.