In the editor when dragging mouse downwards the Event.current.mousePosition.y returns increasing numbers and the Event.current.delta.y is positive. On Android device when swiping the screen downwards Event.current.mousePosition.y returns increasing numbers as well, however the Event.current.delta.y is negative.

Reproduced on:
Google Nexus 5 with Android 4.4.2

Reproduced with:
Unity Version 4.2.2f1 (54f0fc09defb)
Unity Version 4.3.4f1 (e444f76e01cd)