If you made it clear the dice were not always going to decide outcomes, and that you'd be the arbitrator of when they did and when they didn't, then you weren't cheating. Cheating is when you break the rules, and it sounds like you made the ability to determine outcomes separately from dice rolls into a rule.
There are deeper issues here, about communication and game style and character generation expectations, and oversight...etc...but the simple question of whether or not you cheated appears to be 'no.'
Similarly, GM's typically reserve the right to do whatever it takes to keep a game moving, including cheating...so your titular question (Can the GM cheat?) can be answered 'yes.'
In my view.
That doesn't mean that any given use of a rule, or a cheat, is wise or correct...it just validates the philosophy that allows such behaviors. You still have to exercise judgement about when and how to use them.
There are deeper issues here, about communication and game style and character generation expectations, and oversight...etc...but the simple question of whether or not you cheated appears to be 'no.'
Similarly, GM's typically reserve the right to do whatever it takes to keep a game moving, including cheating...so your titular question (Can the GM cheat?) can be answered 'yes.'
In my view.
That doesn't mean that any given use of a rule, or a cheat, is wise or correct...it just validates the philosophy that allows such behaviors. You still have to exercise judgement about when and how to use them.