The checker is a rule engine, not a model
When you paste text into the console, nothing is interpreted by a language model. The page loads a set of functions, each of which knows one way that generated work tends to fail: a credential assigned in source, a statistic with no source next to it, a heading structure that skips a rank.
Each function reads the input, applies a test, and returns zero or more findings with an identifier, a severity and the text that triggered it. The findings are de-duplicated, sorted and weighted into a score. All of it is arithmetic and pattern matching, which is why it is possible to explain every number in the report.
That is also why there is no cleverness to be impressed by. A rule engine is predictable in the way a linter is predictable, and predictability is the feature.