What's happening is that because you are running silentoldconfig, you are going through the configuration again, but instead of using the TUI based menuconfig, you get to do it line-by-line -- at least for whatever bunch of lines it's decided this "oldconfig" updating requires input about. I've noticed this can be quite a few even from one minor version to the next, and I have my suspicions it is a little bit of a broken feature (but then I avoid doing it this way at any cost).
If you create a defconfig and use it via menuconfig, then compile within the same tree, obviously there should be no need for this at all (so the fact that it may happen is a clue to the fact that the mechanism doesn't work properly).
If you later down the road want to use that configuration with a new kernel version, just drop it in and run menuconfig; it will set any new options to a default based on the presumption that you are going to go through and look for them -- or not, as you wish. When you save the configuration and exit, even if you haven't done anything, those differences will be there. One way to check what they are is to save a copy first then diff them afterward.
That "expert mode" option is in menuconfig too; I think it is in the "General Options". If you select it there, it increases the number of other options available (in case you are unaware, the configuration mechanisms never show you anything and everything, they only show you what makes sense based on the current state of the configuration).
Put another way, I suspect your are using that --silentoldconfig switch cargo cult style. It's pointless and will take you on a steeplechase. Because menuconfig does the same thing in the background, unless you like doing things that way (and other things such as eating glass, staring into the sun, etc.), don't. You should never have to. Just leave that switch out.
