This room probably dates from the 1230s, making it one of the oldest parts of the abbey to survive.
Some of the plaster on the walls and ceiling is original and nearly 800 years old. There is evidence of painted decoration in several places around the room. Some of it is medieval, but some is probablay from the 1700s. A later resident, John Ivory Talbot wrote in 1754: 'My painter [Lord William Seymour] is so nice and busy in ornamenting my Cloisters'
After John Ivory Talbot inherited Lacock in 1714, he set about altering the house to suit him. He built the Great Hall you see today at the front of the building and removed the outer walls of the rooms on this side of the cloiser, creating a romantic 'ruin' that could be enjoyed as part of the garden.
The outer walls of these rooms were sympathetically rebuilt in about 1894 when Charles Talbot lived here. If they had remained open to the weather it is unlikely that so much of this plaster would be here today.
-From the sign in front of the room at Lacock Abbey

Yes, they are talking about the Talbot family of photographic fame. William Henry Fox Talbot took this photo at the Abbey in 1835:

William Henry Fox Talbot - Latticed window at lacock abbey 1835 (public domain)