No it isn't, because there are indications that it could be the case and there are no real indications of creationism and many indications that oppose it.
It is very likely that aliens could work in ways undetectable to us if they were advanced enough, humans haven't reached the peak of scientific knowledge by any means. The fact that we can monitor animals and alter them without them knowing, means something out there could do something similar to us. Obviously you are right in that we can't be sure of anything like this but I can't ignore that humans go against the grain of natural history, why would absolutely NO other animal disrupt the balance of their natural environment? Its not because they don't have the capability, they do, we know this from introducing them into eco-systems not designed for them. Species don't naturally evolve in environments that can't handle them, it just doesn't happen, humans really do seem like introduced species. Perhaps not but its as good an explanation as any, the mystery remains as to how humans came about.
If we are an introduced species made by alien genetic engineers someone needs to tell them they really dropped the ball on this one.