I was reading through Feynman Lectures on physics vol II when I came across this paragraph which I don't quite seem to understand:
Since electric and magnetic fields appear in different mixtures if we change our frame of reference, we must be careful about how we look at the fields E and B. For instance, if we think of “lines” of E or B, we must not attach too much reality to them. The lines may disappear if we try to observe them from a different coordinate system. For example, in system S′ there are electric field lines, which we do not find “moving past us with velocity v in system S.” In system S there are no electric field lines at all! Therefore it makes no sense to say something like: When I move a magnet, it takes its field with it, so the lines of B are also moved. There is no way to make sense, in general, out of the idea of “the speed of a moving field line.” The fields are our way of describing what goes on at a point in space. In particular, E and B tell us about the forces that will act on a moving particle. The question “What is the force on a charge from a moving magnetic field?” doesn’t mean anything precise.
But later in another chapter on induced currents he talks about how moving a wire perpendicular to a magnetic field produces a force on the electrons which cause them to move along the wire, generating a current. But he also mentions that moving the magnet itself(and hence it's magnetic field) in the direction opposite to the direction the wire was previously moved produces the same force on the electrons.