I don't have a problem with this.And I think your GM did it wrong. You told him what you were going for, they asked for a roll, you super double succeeded, and the GM then made you fail anyway. Bad form.
I really hate the idea that the players think the can Alter Game Reality. The player says "my character does this" and so "this happens and this happens, By My Command!".
A player should never have a PC take an action, and then demand the result be exactly what they wanted.
This would be a teaching moment in my game of "Ok, if you want to keep the guard quiet don't do something where you LOOSE CONTROL OF THE SITUATION." And also...take out that guard when you take out the tent guy too.