For the sake of argument, let's say that aliens do exist in our galaxy.
The nearest star to us, apart from the sun, is Proxima Centauri which is over 4 light years away.
That's an immense distance, and you have to ask yourself the question, how and why have aliens come that far and then to simply peform right angle turns near to Earth?
Firstly, let's answer the question of how they could travel here. 4 light years is a massive distance, and even if, and this is a huge if, they have managed to travel at the speed of light, that is still 4 years of constant travel. That is also presuming they know exactly where we are, if they simply headed toward our solar system, it could take even longer to find the planet which has the humans on.
The chances are, they haven't developed light speed propulsion, so their journey time would be even larger.