Update. Confused about weight loss while weight training

How do you know you have gained muscle? You can gain strength especially as a beginner without gaining size simply because a month ago you almost certainly were not recruiting all the fibers ova given muscle. Lots of early gains in performance can be neurological rather than muscular.

If you are losing weight you are eating at a deficit, considering your relatively lean starting point it is almost impossible that you are going to add mass anywhere at this point.

Pretty simple. Even though muscle weight more than fat, your using more fat to make muscle. Another words you probably gained about a pound of muscle but burned 6 pounds of fat doing it. Also, muscle tends to stay if used or even get bigger when stressed by hard exercise. The only way you lose muscle is inactivity and over exercising. Fat you burn 24/7 as long as you have a calorie deficit. A pound of muscle also burns more calories to stay around than a pound of fat. It's a small amount per hour. But when you begin to add pounds of muscle and factor the hours in a day and the days in a week it adds up. The more muscle you build the more fat you burn as long as your not eating more than you should.