Here's a different 3 ply Shetland Yarn. Two strands of White and one strand of Black.
One skein is 4,3ozs. with 96 yards. The second one is a mini sein 1oz., 29 yards. Sometimes when you are spinning yarn there is too much fiber and the spool is all filled up. Bit not enough to make a full second spool. So you get a mini.
You wouldn't see such a "mistake" in commercial spun yarn. But it can happen easily with handspun. Makes creating yarn just that much more unique.