It looks like he's mentioning both gym lift and contest lifts through various point in his career so the numbers don't seem too far fetched.
His last official Powerlifting meet numbers were -
Squat 215 kg, Bench 200 kg, and Deadlift 310 kg.
The #500+ bench is the hardest to believe, but if it was a bulked Arnold, and a sloppy gym lift, maybe. I haven't seen any official meet reports that put him over mid #400's.