It does matter, because to get a comparable number from sudo you'd have to count libc. I don't know how many lines of code that is exactly (and e.g. musl or OpenBSD libc is probably smaller than GNU, so there isn't a fixed number to start with), but I bet it's roughly a comparable number, or at least much closer.
As a general point I agree with you, but both sudo and sudo-rs are pretty large.
libc is used by the entire system. It's not a vendored dependency of just sudo. At best, you'd amortize it over everything that uses it to get a reasonable comparison.
Are we not on the trail to doing the same with rust, at least in theory? You don't think someone somewhere has the idea to make an all-rust system eventually? Even without that evetual ultimate expression, if you have even a few rust components in your system and not just sudo alone, then the same point stands. You don't count rust itself any more than you count gcc.
As a general point I agree with you, but both sudo and sudo-rs are pretty large.