That snake has been measured at somewhere betwen 20 and 23 foot if I remember correctly.
In one shot with some people sitting on it it can be seen that it is not that large.
Also in the closeup with the head it is evident that it does not belong to a 50 foot snake - typical head size for a 20 something foot reticulated python, same with the girth that is not even that impressive for a snake of that size but p. reticulatus is a rather slender snake as far as the really big snakes go.
In the wild these will usually feed on animals that do not exceed a weight of 100 pounds - there is a limit to how much their jaws can expand in order to accomodate larger prey.
There was one snake on a show called "Wild Things", and it lived ina cave, it was measured at around 24 feet. This snake looked bigger, and longer, a whole lot bigger than the one on Wild things...
unless it's been measured on camera and independently verified, one could be skeptical...but that head is huge...in the first shot. I don't think Animal Planet is into bullshit claims