WaterMeths, if you are having further tests... see that as a good thing. It means they want to give you a medical but are ruling something else out first.
ECGs can have all manner of different variables. An old family friend had his Class 1 suspended back in the 80s when he was working at CX because his ECG had issues... came back to the UK and saw a cardiologist at the CAA who had no issues with it, and said it was almost certainly down to the location of the ECG leads.
Having had it done in Hong Kong, where the locals have different body proportions to westerners, (particularly this guy who is quite lanky) the leads in the wrong place will have picked up different signals to what were expected.
I had an ECG once where it was picking up no ventricular contraction at all. Another where it had ST elevation. In both cases the doc disregarded it, turned the machine off and did another test at the end of the examination with new leads and sticky tabs, no issues.