Unfortunately, that's somewhat common here. The drinking culture is slowly dying away, but it still persists. It kind of verges on hazing, where anyone new at a drinking party, even a business one, is forced to drink more than they are comfortable with. Luckily as a foreigner I am somewhat exempt from it, but even I get the pressure sometimes. It might be a bit of positive racism, but I get the "you are a foreigner, so you must be very strong against alcohol" thing that I think is probably relatively common, the implied suggestion here being that I should prove I meet the stereotype. Navigating this without offending the Japanese social customs can be tricky.
I don't have a problem with drinking per se, it's pushing it on others I don't like, *pushing anything on others doesn't sit well I guess...like religion or political ideologies as well.