Not really. The truth is that he was a subject who followed the king's orders. Not so cut and dry, but Arya can't understand that. In her little world of honor, she thinks everyone should die or face whatever kind of punishment instead of doing something dishonorable (like her father did), even if they really had no choice. It's the same failure in understanding that lost her older brother the war and got him killed. Most people don't work like that. If he had killed the boy out of his own free will, that would have been one thing, but that's not what happened.
...
Hard as it may be for you, the saying "don't kill the messenger," comes to mind. Be upset with the person who actually caused your problem (i.e. "sent the message"), not the person who had to carry out orders or else. I can understand her anger at Joffrey. He's the reason why her friend died, not the Hound. So far, out of his own free will, he's done more to help children than hurt them.