IIRC the slides on the 777 use a gas bottle inflation, normally the slide pack needs to drop over the door sill a certain distance to pull the pin on the bottle and thus inflate. But it is possible that impact/damage could set one off in the cabin.
IF the doors were opened with an obstruction outside, then it could send the slide into the cabin, however in THIS particular case it seems it happened while crew were still seated (I would guess at one of the impacts) Any mention of which doors? I don't think it would be L4 as that door can clearly be seen detached from the aircraft- however that slide could well have inflated as the door was pulled from the aircraft- but I don't see one or evidence that there was one from the (admittedly grainy) pictures
Normally, manual inflation can only be done once the door is open, via backup manual inflation handle located on the door sill (only visible when the door is open with slide deployed )
Last edited by givemewings; 8th Jul 2013 at 18:34.