It is, and spelled correctly since he was in the US at the time. Had he been anywhere else, it would have been a "butteload" or a "buttloade" (I can't remember which, this is a friend's joke).
The drinking water on board sailing ships was stored in a butt, which had been scuttled (holed) to withdraw the water. Sailors would gather around the scuttled butt to take their water ration, and exchange rumors and gossip, which was shortened to "scuttlebutt".
This has a direct analog in the office water cooler.
It is therefore also entirely appropriate to measure information of dubious provenance in terms of buttloads. That is easily extended to time spent on the Internet, for obvious reasons.
Assloads, on the other hand, refer to the use of donkeys as a pack animal, and would be more appropriate for non-pourable items, which could be balanced across the backside of the animal, or strapped on (to a pack saddle).
I am, sadly, unaware of the history behind the fuckton, or its metric equivalent.
...and a 'water butt' is probably how rural folk in England best know that term. A 'water butt' filled up with rainwater from the gutters was what you used to water the garden with, drown excess kittens in and so on.
Oddly, growing up with 'everyone' having a 'water butt', a 'butt' was a big container full of water, only with the internet and the consequent invasion of Americanisms have I learned a 'butt' is a 'bottom'.
