I experienced the same thing when I finally started to eat lots of food, I always had thought that I was eating lots but I really wasn't. One day I decided that I was going to eat 6 eggs, 4 peices of toast and oatmeal for breakfast and 6 eggs with a couple large glasses of milk at night. With just these changes in my diet I gained 15 pounds in about 7 weeks(175-190). I didn't think it was possible to gain this fast without gaining huge amounts of fat but I remained fairly lean and my strength went way up(added 35lbs to deadlift). Ofcorse these were nebie gains but it was nice !
Half muscle half fat would be about right for bulking-anything better is a bonus.
And the calories work out to about +1900 a day and 128 grams of protein. That would theoretically be plenty to add on that weight, although that much milk might be giving you a little more subcutaneous water.
Oh, yea, and a decent way to tell if it's mostly muscle it to measure a bodypart that you may be training but not necessarily "prioritizing" such as the forearms and calves. 10 pounds of solid muscle evenly distributed would be about 1/2 inch on the forearms or 3/4 inch on the calves.
Not really, if you haven't been training those areas they're not magically going to increase, especially in the beginning stages. Once you start moving heavy ass weight that taxes your nervous system significantly, everything will start to grow.