It means the CA just set the dates to those dates they specifically wanted.
It looks like it's the certificate of one of Let's Encrypts own Certificate Logssystems. Let's Encrypt can sign their certificates the way they wanted. They themselves are not limited to the specific rules we are. Like, when we want a certificate from Let's Encrypt, almost everything from the CSR is ignored. We're getting a certificate with a validity of 90 days from the moment Let's Encrypt issues it (minus one hour for clock drift I think). However, Let's Encrypt doesn't have to apply those rules to themselves. They can issue certificates in the future like this one if they'd like.
By the way, it's issued by this root certificate: crt.sh | 1476662614 Probably the one place that certificate is valid, is in the Certificate Log itself and perhaps other LE logs 