One might argue that it’s a problem if any students need more than 4 years to graduate. However, compared to other institutions, UC Berkeley’s 4 year graduation rate is not bad. https://www.usnews.com/best-colleges/rankings/highest-grad-rate
My S23 is an EECS major, and it’s pretty easy to graduate early in that major; the department actually posts 3-year and 3.5-year sample plans along with the standard 4-year sample plan. But it’s also not uncommon for students to intentionally stretch out their classes over four years, in order to take advantage of additional advanced classes.
I would be surprised if students wanted to buy lecture notes for CS classes, since the lecture videos, slides, and lots of other materials are posted online, so it’s not difficult to follow along even if you miss lecture. It seems the same way for all the other large STEM classes my son has taken. Maybe he’s talking about classes in other departments? Or maybe it was a while ago that you talked to this classmate.