You're right of course, about Ch4 and the BBC, but it is salient to point out that the Beeb also funds a great deal of what Ch4 churns out. S4C (the Welsh version of Channel Four) has many of its news and documentary programmes funded ENTIRELY by the BBC, this is why they do simulcasts in Welsh with the BBC on occasions (such as Live8 and Children in Need).
Added to which, a friend tells me that BBC world is looking into showing the unedited version of the Ch4 doc (in North America).
I don't know how the funding panned out on this doc but the Beeb is certainly not unknown to part-fund this type of doc.
I always think it's a bit odd that the Beeb has its fingers in Ch4 pies, since their remit is so different but, hey, maybe that's the way that the BBC do 'investigative journalism' these days, since they don't seem to do it much on their own channels!