Have you sent the sample out to see what a mass-spec can make of it?
In order to see THCA on an FID, your chemist would have needed to derivatize to prevent decarb. if they ran the control and the derivatized peak is clearly derived from the THC peak (THC gets smaller in derivatized sample. Mole fractions add up correctly), then one has to wonder if you’re even dealing with distillate.
What was the ratio of THC to THCA? Is THCA in distillate a common occurrence? I would expect to see <LOD. but admit that I haven’t gotten to sending my stuff out for 3rd party yet.
Is your current hypothesis horribly botched CBD run or biomass/crude mislabelling?