Not necessarily. It sounds like there is no proof of what caused the cyst to grow back, so I think negligence is going to be hard to prove. However, if you need to have the surgery done, you should regardless of whether it grew back on it own.
Unfortunately most cysts can regrow under certain conditions. If you are concerned the surgery was not done correctly the first time, thus requiring a second surgery, I would encourage you to get a second opinion. Good luck
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