The first living cell would probably occur in a veritable soup of organic matter that it could use to grow off of. However that isn’t strictly a requirement as we know of a number of microorganisms in extreme environments that live off of inorganic matter with sufficient CO2 available to synthesize their own organics. The objection is so simplistic as to be laughable and demonstrates the ignorance of the writer.
You’re going off derivative speculations, without even realizing it. I know it’s difficult, but try to go before that.