I pasted a subset of the Fil-C source code into your tool and it says 6 person years. I just pasted the compiler pass and the obvious parts of the runtime.

Note that I started the project in Nov 2023 and can only work on it maybe 1-2 hours a day because it's just a side project.

So I think your tool either estimates based on very bad programmers, or it's just wrong. Or maybe 10x programmers are real and I am him

Here's more about the COCOMO model it uses: https://dwheeler.com/sloccount/sloccount.html#cocomo