Aren't Lexus and Toyota basically the same thing? Lexus is Toyota's luxury brand, and Lexus cars are built in Toyota factories [0]. Why are they considered two different brands for this? (and, more interesting, why do they have different reliability scores, apparently swapped from last year?)
"Same factory" is used with a lot of things as an argument that things are the same. Industrial processes have a lot more to do with decisions made for the specific product. A luxury product could involve a longer more in depth QA cycle, tighter tolerance for rejection, etc. A commodity product could have more reliable parts because they simply made more of them and had more experience with problems and fixes. The building a thing is made in or using the same machines does not result equivalent products.
Because they're different brands. Volkswagen own Porsche and Audi, but they're listed separately and presumably they have different reliability levels. There are also different reliability levels across different models, but they drew the line at brands.
[0] https://en.wikipedia.org/wiki/Lexus