I beg your pardon. Perhaps this might help…
Your link shows a ‘conventional’ right hand system.
Unreal is not conventional right hand. It is a left hand co-ordinate system. If you draw some debug lines for the world co-ordinate system you can see this clearly. If you build a model in 3Dmax (right hand system) then it will appear in unreal as a mirror image (so you have to set export parameters to overcome this).
Unreal physics is also buggy/inconsistent in this respect. You can even see this in the editor where a +ve rotation about X is clockwise viewed from the origin. A +ve rotation about Y is clockwise viewed from origin. But, a +ve rotation about z is anticlockwise viewed from origin.
This question from Henry Read talks about the inconsistency of the unreal system. (outstanding from 2015)
I, myself am using ‘add torque’ to rotate a complex object about its center of mass and whilst it will complete rotations around Y and Z axes, the rotation about the X axis works halfway and then the Z co-ordinate of the center of mass starts to wander badly.
In short, The handedness of co-ordinate systems and rotation systems are purely conventional and unreal uses its own conventions. Why unreal chose to do it the way they have beats me. It is a bit of a pain really.
Plus there are some gotcha style bugs in their physics I believe but that is really another issue.