I have the same suspicions as you, and figured at best I'd have a difficult to grow ventricosa.
I've not seen the intermediates on ventricosa x lowii so I cannot comment on that. I got the cutting from an unknown donor at the BACPS meeting about 9 months ago. There are usually a few hard-to-find cuttings there, so that it's unusual is not, well, unusual. Nevertheless, I agree with your assessment, but cannot explain why it would be mislabeled. Oh well, I guess as it matures we'll get a better idea of what it is.