Isn’t that the same argument as “Jesus did X. Jesus is a good person. Therefore X is good.”? Is it not the christian philosophy that virtue is doing what God does, and sin is doing what the devil does?
Yes, but the key thing to note about that is that God only does good, while humans do both evil and good. So if you try to apply the standard that works with God to humans, or you will get flawed results. Garbage in, garbage out.
That is not correct. The philosophy is that righteous behavior is what God tells us is righteous behavior for us and sin is what God tells us is sin. God is not bound by the rules he imposes on us humans any more than adults are bound by the restictions they impose on infant children. Thus, there are things God "does" which would be a sin for us to do.