“He wasn’t ordered to be stationed there by his superiors.”
Does not matter. He made the decision based on his situation. That was within his authority to do so.
You are making excuses for what Anderson did, so that you can justify what followed as having the imprimatur of legitimacy.
Washington DC did not send him to Sumter. He decided to do that himself for tactical, not strategic reasons. The Fort was of no value to the Union other than as a bone of contention. It had no significant purpose to the defense of the Union.
"The plan succeeded. They attacked Sumter – it fell, and thus, did more service than it otherwise could."