And yet.......... no synlube is spec'd by any car maker.
GM 6094M is not the the synthetic oil spec so if your owners manual says that then is came with mineral oil, not synthetic.
GM4718M is General Motors' High Performance engine oil specification. Oils which meet GM4718M tend to be made from synthetic base stocks, so it is often referred to as a "synthetic" specification.
However, not all oils, synthetic or otherwise, are capable of meeting the stringent requirements of GM4718M.