Won't speculate on the bump as the more pressing issue to me is how you think those pictures show a horse who has gained muscle?
They clearly show a horse who has lost both condition AND weight.
And yes, she has lost weight because she's nursing a foal. We are feeding her 3 2 quart full scoops of high-protien grain 3 times a day, she has 24/7 access to grass, she also gets two flakes of hay twice a day. So stop judging and claiming that we are not taking care of our horses when you don't even know their diet.