Your original description (knocks, pings, etc...) is a textbook description of insufficient octane. If your car was broken, it wouldn't have fixed itself on your next tank of gas. That's one reason that you got the kind of response from the oil co. that you did. Another reason is very likely that you were not the only one to report the problem.
How long was it between the time you filled up and the time they checked? A busy station can turn over a load of fuel in a few days. While it's good that they're still checking for contamination (water or something else), if the cause really was a load of bad gas, it would be long gone by the time they checked.
I wouldn't worry too much about it. If your car went back to running normally, it's unlikely that any damage was done. I've had the same thing happen a few times. As long as you take it easy on the engine when it knocks, you won't break anything.