The BitTorrent Sync Android and iOS apps seem to follow the BitTorrent.com privacy policy which states explicitly that they gather data such as total traffic and performance metrics.
We also aggregate some data from the BitTorrent Client regarding total
traffic flows and content delivery performance.
I don't see any problem with that; it's completely understandable. This data can be useful to them when further developing the protocol, helps them understand P2P performance in the big picture, and, perhaps, to measure their own value as a service.