There are some places that stock ponds with trout in the winter, and they would have to get them out in the spring. I guess it's possible that they just drained one and they went into the Mitchell drainage and this one went all the way to the lake, where you caught him. I don't think he could have survived much longer.
That's about the most unusual catch I have ever heard of in Alabama!
He is likely dead he was not doing well when I released him. He was probably 14"long