There's a lot of stuff I could say about that, and guess what, because it's Friday I'm going to !
You are right about the forces involved in objects changing velocity in that way. the g forces would be so huge any human inside would be squeezed into a nasty mess. However, one point I would make is that we don't know whether anyone was actually inside that particular "thing". It may be that if they are aliens they have two different types of vehicle, ones they actually travel in and ones they use as robot drones. The robot drones may behave in completely different ways that the ones that beings may travel in in terms of performance like changing position/direction etc. Still I agree in order for the robot drone to behave the way it does, it would still need to use some physics beyond our understanding.
I think re travel through space, it's a technical point, but an ability to manipulate or shield gravity would not actually help that much in interstellar travel. It might help us more easily get off the planet, and construct huge spaceships for long journeys, because it would make building things on earth and putting them into space much easier. But what it wouldn't do is enable us to close the distance gap to other stars in any way. The distance gap can't be closed by overcoming gravity (or at least as we understand it). It can only be closed in three ways.
One is to go very fast, either up to or over the speed of light. This is something we currently believe isn't possible, and accelerating up to light speeds or near to them would take a huge amount of energy - we'd also have to find a way of slowing down when we got there. Even then, the nearest planetary systems would be years to decades away.
The second way is to somehow reduce the distance, by say for example travelling through another dimension, again currently not thought possible. An easy way to imagine this is like an ant on a piece of paper. It lives in a 2D world, can only walk on the surface of the paper and the only way it can get from one edge of the paper to the other is to walk across it to get to the other edge. However in a 3D world, you can fold the paper into a U shape, give the ant a flick and it could fly across the gap, making the actual distance it moves a lot shorter. The ant would be clueless about how to do this of course because it only knows how to walk on the 2D surface of the paper!
The final way is to make the time it takes to travel the distance unimportant or irrelevant to the thing doing the travelling. This could be done via suspended animation (like in the Alien movies) or by making or having your lifetime very long, so a multi year journey becomes less significant in terms of your total lifespan. You'd still want a hell of a lot of box sets to watch on the journey though.