I think you are right, we should fight back a little on this. Nissen is the lead investigator on a trial using corn oil, an Omega 6 yet he can come out and say negative things about an inert mineral oil. I don't think you need to just look for issues with placebo corn oil, but corn oil in general.
Corn oil has an omega-6 to omega-3 ratio of 46:1, which can contribute to this imbalance (1). Summary Corn oil is 100% fat and provides 122 calories per tablespoon (15 ml). It's mostly made of polyunsaturated omega-6 fats and contains some vitamin E.