Conveniently, the writer defines Christianity in distinctively non-Biblical terms. In his mind, JWs aren't Christian because they reject a particular teaching that he interprets into the Bible. A teaching, BTW, that the Bible never actually explains and requires a lot of glue and paperclips to keep together.
I'll let the believers debate whether or not the Trinity is true, but the definition of Christian is a follower or believer of (Jesus) Christ. There are any of a number of ways that belief can be taken, and seemingly endless interpretations of what is correct or incorrect doctrine.
Also... a Catholic criticizing the sordid history of ANY other religion?
I mean coooooome oooon!
At least JWs only look bad in terms of contemporary religious experience, which has mostly become neutered in the developed world after centuries of struggle. Catholicism has a very long and evil history, including endless scandals they're guilty of in the century and a half since Watchtower has come into existence. The whole "damn! look at that messed up religion!" thing is hypocritical and ridiculous.