But isn't that a good choice, considering the limitations of the study?

Yes. We should never make claims of fact that we don't know to be true. The authors of the study know this, and I'm sure they've been careful to say, "here are the data", not let's figure out why this is the case. The media are typically the ones who get in the way.

I find it interesting also that my vegetarian friends are so offended by it; while I reposted it because I found it interesting, I certainly wasn't trying to pinpoint those individuals and say that they have lower qualities of life.

Yes, but they are probably already sensitive, because people probably tell them from time to time that their life choice is stupid. They likely see it as an attack on their lifestyle, and can't see it as just an interesting dataset. It's like if you're a Christian, and I tell you of a new study that says that Jesus probably wasn't a historical figure. You might get bent out of shape about it, even though there might be other good reasons why being a Christian works for you. Not a perfect analogy, but I think there are some parallels.