The cast off appearance may just be an effect of the shadows. That said, I have seen mountain rifles with cast off as well as cast on, but someone on here pointed out a while back the possibility of the thin wrists warping on some of these old guns as they sat upright in a corner over many years. I don't know if this is the case, but there are definitely examples with cast whether intentional or not.
There are a number of mountain rifles that look to have been built as 1/2 and 3/4 stocks, and some that were cut back later. Sometimes, if the bottom of the barrel was not dressed out as smoothly as the top, we assume it was originally a fullstock. Hard to tell in this case - it looks like there was some work done in front of the forward cap - to both the underside of the barrel and the wood - after the barrel was browned. So I would guess this one was a fullstock originally, but hard to say.
Guy