Yes, this folder contains a private key and a certificate for quic.clemente.io.
Unfortunately we need a valid certificate for the integration tests with Chrome and quic_client. No important data is served on the "real" quic.clemente.io (only a test page), and the MITM problem is imho negligible.
If you figure out a way to test with Chrome without having a cert and key here, let us now in an issue.