Yeah as I said it was a tongue-in-cheek comment and I don't believe it, just wanted to provoke some discussion. :-) But in any case what I meant is that TeX/MF are among his biggest programs (that I know of), not that 20000 lines is a large program (he calls it "medium" IIRC).

(Ironically, in my previous job supposedly using "modern" programming practices, a single Python file had organically grown to over 25000 lines in length and people complained to GitHub about the file not being rendered in full in the browser.)