When I was an intern I was 100x better than I am at this point in my career.
The basic atrial fibrillation and STEMI is something any doctor can interpret with confidence (I used myself as an example as I'm probably the least competent because I haven't looked at an ECG in 10 years). I doubt non-cardiac surgeons are much better on average as they don't really look at these themselves that often other than for basic things.
An ER or general internal medicine physician is expected to be competent in more advanced but common stuff like bundle branch blocks, left ventricular hypertrophy, non ST elevated MI.
Weird arrhythmias or conduction abnormalities is really only for cardiologists, and even then typically a subspecialist electrophysiologist.