Nah, doubt it. The fish closer to the surface got fried, but that lake surely is deep considering the giant fish that leaped out. What he killed likely isn't even within a margin of error for that lake. I mean, that single giant fish probably eats that amount over the course of a weak if not day (a an orca can eat up to 230kg a day, for example, to show a similar sized predator).
Nature is filled with mindblowing numbers. You'd be surprised.
Besides, electricity would extremely quickly discharge over such a huge body of water, and not that far away from the point of impact, the fish would start being less and less affected. Some of those fish seen probably got paralyzed instead and if left alone would get back to 'life'.