That seems like alot of shift in 3 weeks to me, just based on what other people have shared of their training logs here. Are you lifting really heavy, to failure, or just weights that are heavy but not 'i can't do another rep' heavy? IF you are just lifting I would say def not and that measurements can be inaccurate. If you are lifting to complete failure and throw-up exhaustion with HIIT cardio, then my answer becomes - maybe?
I think I've been able to put on 3 lbs of muscle in about 3 months, and that's with really changed eating habits, super HIIT cardio, and cannot-lift-another-rep weight training. Also known as Body for Life. And even those are just estimates, it's really difficult to tell without being bodypodded or immersion tank tested.
But it's great that you're seeing progress! Even more important than building muscle imo is to shed the fat, and that you can def tell by how your clothes fit.