Not sure what your local lab means in context - is it just perhaps your clinic or a smaller local hospital?
As a retired RN I do know it’s not uncommon for one place to ask for another opinion. Mayo obviously is an excellent place with much experience in many fields. Good that this was how it’s being handled!
I don’t think it necessarily means a melanoma specifically but perhaps it’s more unusual looking or margins were questionable if it is malignant…wishing you best of luck and wishes!