I only have limited personal experience with this issue, but based on that I think it's not uncommon for some people of Jewish heritage to support the idea that one is/can be Jewish even if you have no belief or participation in Judism. My belief (casual, unsubstantiated by any research) is that this idea might be propogated by the "communal persecution" felt by Jewish people since most of us know the magnitude of suffering that has been directed toward Jews. I suppose this must be a powerful wound that binds people together in spite of other major differences...stick together to survive.
My wife and her extended family are of Jewish heritage but have always been religiously/philosophically atheistic; my brother-in-law was not even bar mitzvah'd. I was raised and educated Roman Catholic though since early college days I don't participate or believe in many of Catholic religious tenents...so I don't consider myself Catholic at all. But when my kids, who have not been raised with any association whatsoever to Judism (or Catholicism), ask their mom "what are we?" she says "...you're Jewish because I am". To bring my confusion even closer to home, I was circumcised when I was 9 years old since my Catholic parents became convinced that it was a good medical decision. No wonder I'm so screwed up ....
j/k I'm as normal as the next wacko.