Gotta admit, found this hilarious: "By the way, if you want to know what I think about this whole reddit experience - NOT BAD!"
Which further confirms that this whole AMA is a carefully crafted PR stunt.
I’m really not sure what you expect. The President has a busy schedule, plus (as the guy running for office) enough money to hire people to do stuff for him.
We all nearly always plan what we say and do. The stakes might not be quite so high for us most of the time – but the principle behind it is the same.
The only difference is that the President can afford people whom he can delegate some of that planning to. It’s very simply not possible to do this any other way.