He said "The data—including what is available through the Pew report— shows that disbelief in God is relatively stable across time and generation." That is not about those "very or somewhat interested in religion"; it's about others. The NYT reporter gathered the data for the others, and showed they are growing, both across time (from 10.3% in 2007 to 15.8% in 2014) and generation (many more in the 'millennial' generation than earlier ones). And the growth still applies if you restrict the definition to just 'atheists and agnostics', or just 'atheists'.
Flory's article is mainly about the people with 'no religion in particular', but to whom religion is still important; but that doesn't mean he can just assert that the numbers for those who aren't interested in religion are stable. But you might think from the way he wrote that there was a more significant increase in the 'no religion in particular but religion is still important' group. Actually, Pew says:
As the ranks of the religiously unaffiliated continue to grow, they also describe themselves in increasingly secular terms. In 2007, 25% of the “nones” called themselves atheists or agnostics; 39% identified their religion as “nothing in particular” and also said that religion is “not too” or “not at all” important in their lives; and 36% identified their religion as “nothing in particular” while nevertheless saying that religion is either “very important” or “somewhat important” in their lives. The new survey finds that the atheist and agnostic share of the “nones” has grown to 31%. Those identifying as “nothing in particular” and describing religion as unimportant in their lives continue to account for 39% of all “nones.”
But the share identifying as “nothing in particular” while also affirming that religion is either “very” or “somewhat” important to them has fallen to 30% of all “nones.”
http://www.pewforum.org/2015/05/12/americas-changing-religious-landscape/The proportion of the whole population for 'nones' went from 16.1% in 2007 to 22.8% in 2014 (table at the top of that Pew page). So, the 'very/somewhat important' group went from .36*16.1% = 5.8%, to .3*22.8% = 6.8%. The group that Flory calls the 'religious nones' is growing more slowly than those with no interest in religion at all.
I also notice that the headline, and Flory's article, both assume that the 'religious nones' are still Christian, just not keen on the particular churches available to them. That assumption seems unwarranted to me; they could easily be the 'I believe in some higher spiritual power' type.
= new reply since forum marked as read