Hello My 4.5-month-old baby was told that he's quite soft, we haven't…

Hello My 4.5-month-old baby was told that he's quite soft, we haven't received any massage before, all doctors have passed, everything was normal, and I didn't think about it after that, now I started noticing that he's not fully able to roll over by himself, he tries to do something but is not quite there yet. Now I want to take a massage course, I just don't understand what "soft" means, is it muscles? Should I be worried already?