I've been off and on for a few years (PM).  When I first started, I was around 295lbs (at 6'5)  I've lost considerable weight during that time.  Down in the 245-250 range.  My breasts are probably the same size as before, but on a leaner body, they do appear bigger.  And the shape is closer to a female breast than moobs.  So, I suspect weight loss just makes it easier to see your growth.  
The way I see it, take a skinny person and an over weight person.  Both have the same growth.  For visual sakes, let's say they've grown a marble size of breast tissue.  For the skinny guy, lay a piece of paper of that marble.  The marble is noticeable under the paper.  Now the fat guy, cover that marble with a bean bag (the kind you would use for corn hole) you can't tell just by looking that there's a marble there.  the bean bag probably looks exactly the same as if there wasn't a marble.