It could be a GoPro, however the way you view what the camera is viewing is thru wifi, and it doesn't work underwater (one of my few frustrations with my GoPro). If he was viewing it live, which I doubt, he might have been using one of those Ice fishing cameras which do stream live.
I've put my GoPro under water several times with no worries. as long as you secure it, you shouldn't have to worry. Its how you get really good video.
heres a link to one of them. If you look at my channel, you will find another one thats not so daring but still got some good video of a Rock Bass protecting it's nest. https://www.youtube.com/watch?v=KdLX5H3-MFw