I’m with you on being suspicious.
You’ve clearly seen the THC Imposters (Isomers) thread
My recollection is that looking like CBC on HPLC is one of the hallmarks of the mystery peak sometimes referred to as delta10 THC.
you now need them to run your sample on their GC. Or find someone who will.
if their lead chemist won’t watch that video, and then run the samples on their GC, I’d take my business elsewhere…
as for WTF is going on, & how can biomass affect isomerization?
I recall it being proposed that delta10 was potentially an intermediate to CBN, one than might accumulate in the absence of O2.
If you were now to tell us that biomass from source B had been nitrogen sealed then stored in a non-climate controlled warehouse for a year, I might even look like I knew what I was talking about 
AND, there is precedent for high CBC in come high CBD lines (probably not what you’re dealing with).
Edit: Of course, one could also posit foliar application of ?!? (isomerization catalyst) to biomass B at source of origin.