Can you post a pic?

In the 50s & 60s lots of homes had paint that had been applied with a patterned roller. I know that many hallways in Chicago apartment buildings had this applied to the walls to hide marks and create interest. Quite a skill to apply it correctly, that's why a more abstract pattern is a bit more forgiving in application.

They still sell them. You simply roll the patterned paint filled roller over the wall once and transfer the pattern. No seams

If it was rolled with something like that, wouldn't there be a strip along the ceiling and baseboard with no pattern, since you cant get the roller all the way in there. Similarly, against door trim, corners etc...it would be close to impossible to have the roller' s width fit perfectly into a stretch of wall.

could it have been 4 x 8 sheets of melanine? They look(ed) like wallpaper and installed like paneling.