"Exposure value (EV) denotes all combinations of a camera's shutter speed and relative aperture that give the same exposure." (Wikipedia definition)
You're using a different EV if you select an aperture/shutter speed combination that doesn't give you the same exposure. It doesn't matter whether the change is made with the aperture or the shutter speed.
For example, if the the "correct" exposure for a scene requires f/8 at 1/125, then f/5.6 at 1/250 and a number of other combinations will all give you the same ("correct") exposure. These are all EV 13. If you use f/5.6 and 1/125 to move your histogram to the right, you would be using EV 12, but f/8 at 1/60 would also be EV 12; i.e. both give the one more stop of exposure, both are EV 12. You changed the EV in one case with the aperture, the other with the shutter speed.
(The ISO remains constant in all of these examples.)