Yes you are a non secretor. The B12 effect seems to be real but in itself is unlikely to be of great significance.
There are other studies looking at the effect of secretor status on microbiota composition and correlation with IBD, as
@sarah darwins has indicated.
Here is fairly comprehensive analysis which is trying to explain mechanisms.
They took samples (endoscopic lavage, so from the epithelial mucosa, not lumen as would be the case with faecal samples) from 12 -/-, 18 +/- and 9 +/+ individuals and analysed microbial composition as well as microbial and human metabolites.
Their overall conclusion was
Interestingly they saw metabolic differences in +/- as well as +/+ individuals.
Essentially they are saying that the presence or absence of secreted H antigen in colonic mucous has a significant effect on microbiota composition (the antigen acts as a carbon source for some bacteria) which in turns affects energy metabolism in the microbiome of +/+ and +/- individuals. These changes are associated with sub-clinical local inflammation in the host mucosa.