Could abnormal EKG results be wrong?

Yes and no. An abnormal ECG may represent an inaccurate read, ie mistake or not overread by a competent cardiologist. An abnormal ECG may also represent a correct read which is a false positive, very common. In other words, an ECG is not the most sensitive or specific test, and the ECG reading could be correct but doesn't necessarily mean that the patient has this particular pathology, and vice versa. .
Yes. Ekgs, like any test, must be performed correctly. The leads must be placed appropriately and there must be minimal movement when the image is captured. There are a number of scenarios whereby an ekg could be incorrect or have significant artifact.