Yup, I got into Berkeley EECS this way back in the late 20th century. I'd guess it's legitimate load-balancing rather than an attempt to game the ratings. I assumed this meant that my application was borderline and I was grateful to be able to sneak in. The Extension program is a nice transition to college too.

Load balancing is the most likely reason. At any given college a lot of first year students decide college isn't for them or they get home sick and drop out within the first semester. After that initial period student population of the class is much more stable.