To answer the question directly; I don't think it is possible "intelligence" was "brought" by anything; as an earlier answer details, the evidence is overwhelming that intelligence arose slowly over hundreds of millions of years. Our neurons are not functionally different than the million found in a fly or cockroach; we just have a hundred thousand times as many, far more complexly organized, and even then not very much differently than neurons in great apes. Mice and Corvids are "intelligent" and creative problem solvers.
A working definition of intelligence will help us: Not all scientists agree, but a pretty good working definition for AI researchers (including me) is that intelligence is the ability to form models based on observations that let us predict most likely states in the future or past. The more accurate and far reaching these predictions are, the greater the intelligence. Animals with less intelligence can be trapped by animals with greater intelligence; the fish doesn't realize what the hook shape will do in its mouth until it is too late; the human fashioning the hook shape does so with a model of how fish bite and behave, and a model of how the hook (like an arrow) can enter flesh easily in one direction but be difficult to pull out in the other.
In the "past" direction; we have forensics, or something like astronomy or geology: Intelligence, in the form of working models, lets us narrow down what must have happened, to either a singular event (e.g. a neutron star exploded) or at least a small set of possible explanations (e.g. Adam either killed himself or his wife murdered him and made it look like suicide).
Either way; consider it an ability to model interactions, predict the outcome of various interventions, etc. Then super-intelligent aliens may have supervised evolution and intentionally caused mutations they could predict would be key to developing future intelligence. That isn't "bringing" intelligence, more like "creating" it, or the conditions for it to arise.
The difference between causing seeds to be scattered on fertile ground, versus planting already sprouted seedlings.
To our knowledge there is some chaos theory that suggests very far reaching intelligence is not possible; there are too many confounding factors. So likely, if guided evolution is how we came to be sufficiently intelligent to create a civilization (however one might define that, but you know what I mean), then it could be "without a trace", because we have no idea where mutations come from. We think they are chance; but for a super-intelligent race, they may have chosen to mutate genes in ways that were specifically plausible but hadn't happened yet. Or they may have, opportunistically again, arranged certain "accidental deaths" to prune the tree into a shape they wanted.
I'd call that topiary: Some bushes sprout in many directions; but if you want the bush to look like a duck, you can choose to clip branching sprouts that won't fit into the overall pattern you see in your mind's eye. Darwin's unnatural selection model for livestock did exactly this: The mutations in the livestock were natural, but the human livestock managers terminated undesirable mutations, or at least did not let them mate, while desirable random mutations were mated extensively. Aliens supervising human evolution could have done something similar; with greater foresight into the ramifications of each mutation, both physically and socially.