I don't think Amin especially espoused any significant left beliefs. He was always a loyal subject of the British colonial military in his youth, and Britain supported his initial coup as he was less likely to turn to communism. It wasn't until he started hunting down Indians and other Asian minorities that diplomatic relations were severed and the arms shipments dried up. So he did the next most sensible thing and turned to the Eastern Bloc and Libya for assistance, and adding an anticolonial slant to his nationalism, decrying and repudiating the west entirely. It seems the guy was paradoxically apolitical and just chose violent ethnonationalism as the closest thing to an ideology, the rest was just a matter of convenience and pragmatism.