Pies, damned pies, and...
>The statistics are surprising since iOS is generally more secure than Android on account of its restricted application installation controls.
What statistics? All the previous paragraph meant was that "about 40 percent of large enterprises [which being large presumably a fair few iPhones] sampled by Proofpoint" had at least one iPhone running at least one malicious app.
There is no way of extrapolating from that statement what percentage of iPhones have malicious apps installed, beyond "more than zero", so I can't be surprised or otherwise.