I assume they mean a system that uses existing crypto algorithms, rather than building everything completely from scratch. For example, if the system involves a key exchange, followed by the derivation of a shared secret, followed by symmetric encryption, all of these steps could use existing solutions with multiple available implementations (DH+AES, or perhaps X25519+ChaCha20). Wiring existing algorithms together to form a secure protocol is certainly doable by a competent programmer in a weekend. And in the Gopher spirit, if you really want to implement ChaCha20 yourself, that's much more tractable than implementing all of TLS.