I’m wondering why his dynamic glibc C executable is so big.
He's counting glibc too, not just the binary. This is true for all of the examples, the size is the binary itself plus whatever system/libraries you'd need to actually run the binary.
Which version of C?
All versions are interesting, zig/assembly managesto do it in 2/3 so what is musl doing that needs 5? And what on Earth is glibc dynamic doing that it needs 65?