Wait, you let your two month old CIO in the middle of the night? No, you should not do that, in my opinion. It is VERY normal to eat more than once a night at this age. Once a night for a 2 month old is a dream. It's doesn't matter how much your baby weighs, at 2 months old if they wake up to eat you should feed them.
Now, if he really just made a few grunts and went back to sleep, I think that's fine, but you said he cried. I don't think you should use any kind of CIO at this age. STTN is 5 hours of straight sleep, not 11 or 12. Some kids don't STTN 12 hours until they are 1 or 2...then again, most adults wake up at night.