Was the water the same or near the same temperature as his tank water?
I only asked because I also fried one of my Betta's, Gallifrey. The water seems warm to me so I thought it was okay, Let it cool for about an hour by my stick on thermometer which only went to 86 still wasn't reading it. So I figured heck with it! I'll just put him in! So took the net, scooped him up and plopped him in. Flared up instantly and went motionless. i freaked out and scooped him back out to put him into the cup I was using but it was too late
I accidentally fried him, but it was certainly a learning experience.