Need thoughts

I got a ferret from a pet shop called Atlas pet his name is bear I’ve had them for a couple months now. Recently, I just noticed a lump between his shoulder blades on his back. My first thoughts went to microchip. It seemed too linear but I convinced myself otherwise because there is a no refund or live pet return for that store and they get them directly from Marshall Farms. Not saying I recommend Marshall farms there was just none in my area to adopt or at a comfortable drive for one to be in a car being a first time ferret owner I went with it. Bear came with a Marshall Farms birth certificate and was in what seemed like good shape similar to our others diesel who we also got from there. Diesel doesn’t have this lump today. I ended up taking bear to the vet and during the appointment I had asked the vet to feel the lump on her back and give me her thoughts on it. We scanned for the chip first and found that bear is chipped. Now I am confused when we got there. Bear was very small and has gotten a lot bigger. Acted like baby ferrets do. The chip was unregistered. Is this odd do you think that maybe he was returned by someone that bought him before. I called the store and they do not do refunds/returns and from what I can tell Marshall Farms does not chip their ferrets. Not that knowing if he was older or was adopted before would change anything I just would like to know peoples thoughts.