The most common thing I could find when searching "ball near navel" was a hernia. A hernia is not normal, but neither is losing all your muscle within a month. The thing is without an official medical diagnosis it isn't clear exactly what it was--because it could also have been a tumor. When dealing with a hernia, you really shouldn't do any heavy lifting as it can make things worse. It usually takes longer than a month to lose significant amounts of muscle.
I will say that there are many people who claim to be an expert who really aren't. There are also experts who get results in a manner which is not the safest. I had a personal trainer try to teach me to squat incorrectly. However, he was not a personal trainer that specialized in weight training, nor was he someone who coached lifters who compete. At the same time, even though I wouldn't call him an expert, if I told him something was off he would modify his plans to accommodate or if he thought it was something more serious he would have told me to go to the doctor.
There are some risks associated with lifting that you have to consider. The most common risks are muscle strains and joint pain due to trying to do too much too fast or improper technique. It does not mean that lifting is bad, or as inherently dangerous as playing tackle football. Ankle sprains are a common risk in basketball or any other sport where you have to change directions quickly--but that doesn't mean that basketball is to blame for the injury.