thank you for your question.
For full metal crowns, the minimum thickness required for longevity of the crown is in fact very fine and can be circa 1mm with no issues and/or impact to the underlying tooth.
Without fully understanding what kind of crown was issued and the design of the crown, I am however unable to advise you on what this said inner layer may be made of or whether the remaining thickness is sufficient.
If the crown is properly designed and truly intact, there is often nothing to fear even if the deeper metal layer is exposed.
Without a visual inspection though, I am similarly unable to comment on whether it could be a tiny hole in the crown on not. If it is indeed a hole then bacteria ingress is of course possible.
I hope this clears up some of your doubts!