Q: Hi mike when people lose fat sometimes they lose some muscle mass right ? so if someone is losing weight very fast it might not be fat am i right ?

A: That's exactly correct. The slower your weight loss is, the more likely the lost weight is actual fat. Losing weight too quickly can result in lost muscle which in turns greatly increases chances of the fat coming back (because your muscle is a fat-burner so the less muscle you have, the less fat you can burn).