We have not heard of any mobile devices preloading podcast media. What app are you using on IOS7 that you think is doing this?
On the other hand, some apps do not stream content if you are subscribed to a show. they do download the files so they can be listened to offline (this is the main way podcasting works)
If you would like us to audit your stats, use our contact form at blubrry.com and we will take a in-depth look. I'm still convinced that you are just having a bigger audience from what I see on the surface.