1. For whatever reason, Nikon has designed the D3100, D3200 and the D5100 (and some others) to raise the ISO to the maximum in low light situations when you use the built-in flash. The camera seemingly ignores the fact that there is to be a flash and instead meters for the ambient light value.
2. ASA and ISO numeric values are the same. However, there are very few references to ASA values in these modern times, so you may want to tuck it into an old trunk with your film cameras and cassette tapes and put it in a corner of your basement.