Certificate Transparency is a (mostly Google-developed) program which aims to require that certificates be publicized to some third party, so that mis-issuance (just like this one!) can be detected. You do this by telling a third-party log server that you're issuing a certificate for a domain, and the log server gives you back a proof (essentially a countersignature) saying "Yes, I am a third-party log and I've seen this certificate and I'm publicizing its existence."
You can submit the actual certificate to the Certificate Transparency log, but then you don't have that proof immediately, so the certificate isn't usable until after it exists. (And the easiest way to send the proof to a client is to embed it in the cert itself.) So instead, the CT protocol allows you to generate a "pre-certificate", a modified certificate with a special X.509 extension poisoning it from actually being used as a certificate. It is a promise that you are willing to issue this certificate, but cannot be used to authenticate.
Since it can be exchanged for a CT log proof, just like an actual certificate can, it has exactly the same verification / trust requirements as actually issuing a cert. However, it cannot be used as a certificate.
Chrome now requires Certificate Transparency for all CAs that it has authorized to sign extended validation (EV, green bar with the company name) certificates, as those are held to a higher standard than the rest of the CA system is (currently) held. While Google also operates the logs, they shouldn't have needed any special access: any website operator can ask the logs "Hey, what proofs have you issued recently," and cross-check those against the certificates they actually intended to get signed.
