There is absolutely nothing in this article that ties the drop in religious affiliation and the internet other than a correlation. Its not worth the paper its written on (or the pixels its written on . . . .).
My personal theory is that Progressivism is a quasi-religion which has had its dysvangelists in education (at all levels) and among the elites for more than a century. Certainly a great many Catholics are really Progressives, and the Episcopal Church in the US has gone from the old jibe, "The Republican (or Tory) party at prayer" to the place where Progressivism finds liturgical expression.