Kind of a shoddy analysis. This phone is really popular and selling well. That a higher percentage of buyers are not switchers doesn't mean that the phone isn't popular for switchers -- merely that it's ALSO very popular with non-switchers.
The last release was a "tock" release, perfecting the form factor rather than renewing it. This is a "tick" release, which will naturally attract the early adopters that have already been set on a 2-year refresh cadence.
In other words, many who bought the 4 and then the 5 are also buying the 6 for similar reasons (new, shiny). This means more "non-switchers" in the field.
To detect the effect on switchers, you'd need to first correct for volume and then compare that. Let's say they're 10% of 50M handset sales now, vs 15% of 30M in sales last year. 5M handsets v 4.5M handsets would be a 10% increase in switchers due to form factor.
(This number is a fictional example. I don't have sales numbers on hand and don't feel like looking them up. I'm not a professional sales analyst.)