Punishment really only comes into effect when you have been repeatedly reported for the same thing, and if a reviewer determines that your negative behavior is consistent.
From a narrow view, if something like this happened and you apologized in chat, it will probably be determined as a mistake and you will not receive punishment.
However, if you repeatedly forget Smite, or repeatedly doing things that automatically put your team at a significant disadvantage, even if you are sure to tell your team that you are sorry, it could be determined that you trolling, but saying sorry to cover up.
I wouldn't be too worried if things like this happens occasionally.
Just do your best to keep it at a minimum.