you would be lucky to gain 10 pounds of lean muscle mass in a year. significant fluctuations in weight like that are usually attributed to water retention/improved hydration as a result of dietary changes. however, muscle memory plays a role in that you can regain muscle that you have had and lost in the past fairly quickly... but not in a week, usually over 4-6-8 weeks.
usually its a combination of factors anyway.
just stick to your plan, ignore the scale and be consistent in doing your thing
