I believe that they were called a butt because the way there were packaged. I think they were packaged/transported in some sort of barrel that was called a butt and so they ended up be termed as butts themselves... not sure where I heard that though so take it with a grain of salt.
You are absolutely correct! From Wikipedia:
[h1]Boston butt[/h1]
From Wikipedia, the free encyclopedia
(Redirected from
Pork butt)

American cuts of pork
Boston butt is a cut of
pork that comes from the upper part of the shoulder from the front leg and may contain the blade bone.[sup]
[1][/sup] Smoked Boston butt, which is then pulled from the bone and served with or in a spicy sauce is what is commonly referred to in the American Deep South as
Barbecue.
In the United Kingdom, Boston butt is known as
pork shoulder on the bone as regular
pork shoulder normally has the bone removed and then rolled and tied back into a joint.
[h2]History of the name and cut[
edit][/h2]
In pre-revolutionary
New England and into the
American Revolutionary War, some pork cuts (not those highly valued, or "
high on the hog," like loin and ham) were packed into casks or barrels (also known as "
butts") for storage and shipment.[sup]
[2][/sup] The way the hog shoulder was cut in the
Boston area became known in other regions as "Boston butt". In the UK it is known as "pork hand and spring", or simply "pork hand".
In Spanish the cut is known as
paleta de puerco,[sup]
[3][/sup] and is the main ingredient in the famous Mexican dish
carnitas.[sup]
[4][/sup]