Well, one point you made had merit. It is possible for a loose connection to give the same basic symptom as a weak or dead battery. While it could cause the no-start, it wouldn’t result in the damage described.
Having owned a positive earth car (MG Midget) can I ask you what the disadvantage was with them? I had the feeling that when the change to negative earth came about it was more for falling into line with the majority than anything else.