So true.
When I was inactive and completely out of shape, I actually weighed less than I do now when I'm more active. And that's without even deliberately bulking.
When inactive and living a sedentary lifestyle, like most people who will use a scale, it isn't good. Your body composition (muscle, fat, water, bone density, etc.) changes slowly over time without you realising and before you know it you're out of shape. So your weight may stay the same even though you became fatter and lost muscle.
If your diet is in check and you're trying to lose fat, a decrease in the scale weight IS good. It's unlikely that your muscle gains are going to counteract the weight lost from fat, since muscle growth, realistically, doesn't happen that fast, unless you're a complete beginner