You are being overly pedantic and arguing for the sake of arguing. The rhetorical language you are using "might make more sense" and "easily verify" is demeaning and insulting and doesn't add to the discussion.
311 is the first course of the major and is also by the sample of folks in the reddit discussion also the hardest, covering the most advanced material in the shortest amount of time. It is a weeder course for the major. The 100 level classes are open to everyone.
Your argument might make more sense if 311 were the first CS course, but it's not. You can easily verify that by looking at the course listings which reveals it has a prereq, CSE143, which has a prereq of CSE142. So short of skipping those, it's the third course at the earliest.
https://www.cs.washington.edu/education/courses