Correct[0]. This was also my first thought after reading

> Unfortunately, unlike many other languages, SQLite has no formal specification describing how it should be parsed. It doesn’t expose a stable API for its parser either. In fact, quite uniquely, in its implementation it doesn’t even build a parse tree at all9! The only reasonable approach left in my opinion is to carefully extract the relevant parts of SQLite’s source code and adapt it to build the parser I wanted

Did they made a proper problem research in the first place?

[0]: https://sqlite.org/lemon.html

I was also baffled. "No formal specification"? Two minutes of browsing is enough to find it: https://github.com/sqlite/sqlite/blob/master/src%2Fparse.y