Looks real. The guy's pastebin rant mentioned Simatic by name... another summary can be read on Joel Langill's blog...
Similar to the Springfield attack, this one had HMI-level access which from what we see on the screenshots, could have caused more damage than just burning out a pump. The Springfield attack followed a breach of the integrator's database containing site remote access url's, usernames, and passwords, so the attacker just "walked in the front door" so to speak using their credentials.
The Houston attack looks like more of a direct assault.