I have a group that I used to play w/ on a regular basis, until I moved away. Since then, I try and play through skype when I can. I was the gm for them for about 3 years, running various systems. I would never let them take back a move. People need to deal w/ the consequences. Heroes make mistakes. Life happens.
Since I have moved away, and they have taken turns as gm, or found other gms, I have learned that anytime someone messes up, or "accidentally" does something detrimental, such as your above incident, they all just say something like "that didn't happen" and redo the whole scene. A few months ago I was running a homebrew dungeon through skype for them, and when I would not let them take something back they all proceeded to get pissy and mopey and I forced them to deal w/ it and move on. We never had a second session.
Players make mistakes all the time, so do gms. People need to take the time to know everything about their character, and everything that they can do. A player should not, in my opinion, be running a spell caster is they do not take the time to study and know every spell first.
As for what you did, I totally agree w/ how you handled the situation. If the player would have taken the time to read the spell through, he would have worded his commands differently. I have a player right now that is running a half-elf barbarian. Since first level I was always wondering why he was dealing so much damage with his off hand attack, but since he was crit failing more than anything, I let it slide. When he reached third level he took the feat that allows you to add your strength mod to damage w/ off hand. The other players helped him choose it, and when they did his response was "You don't add strength mod into off hand attacks?" People need to know everything their characters can do, and cannot do.