Note that project is the outlier for how much code it contained. That team did have the most trouble getting things done on time and fixing all the bugs, so they passed the least tests, as one would expect given how much code their design choices required them to write. I think the causality goes from their design to the line count, not from the line count to worse design, they had to write lots of code to implement their more abstract design choices. I looked at their code and didn't see any obvious deficiencies in anything other than the design.
Also note that UWaterloo's CS and SE programs are different than other universities. Everyone on all teams had at least two years of full time work experience at 6 internships. The people I talked to were also programming enthusiasts who read online a lot. The only teams that may not have written the most idiomatic code are the person who used Python alone, and the Haskell team because I've heard idiomatic high-end Haskell involves an insane amount of knowledge of abstractions like lens, way more than all the other languages.
This compilers class is also well known for requiring lots of work, so students often arrange their schedules to have a low load from other classes while taking it, which is possible since the CS program requirements have a lot of flexibility.