Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
You also have to remember Golurk's 3 immunities. It can easily switch in on Normal Fighting and Electric attack attacks, making it a nice check to many choice users such as Braviary and Emboar and even, on occasion, bulkier pokemon such as body slam Lickilicky.
I am pretty sure that that is the contrary ability activating. Contrary reverses stat changes, so if a move such as leaf storm lowers your sp atk it will raise it instead. On the contrary (heh heh) if a move such as charge beam raises your sp atk it will lower it instead.