Sounds like a win to me.ok so he found someone to take the gold fish... and he is getting a 10g for the 3 danios a tetra and a redtailed shark.
That's perfectly fine for a ten... Just tell him to ditch the cories. But he does need to sell the other fish if he wants those...
If he has started reading online about fish keeping, it is a step in the right direction. He will continue to make mistakes that will drive you nuts, but think of him as in his infancy (so to speak) in the hobby. Children make all kinds of mistakes that drive parents nuts.
Don't wig out on him and you may help to guide him through this and make a true fish keeper out of him.