So many problems with "100% coverage". Even if you measure it as branch coverage, it only indicates how much of the code that is already written has been covered. It doesn't tell you how much code that is missing, eg guards against malicious input, null-checks or other out of range arguments. This reason alone should be obvious enough for anyone to understand that the metric is completely bogus.
As others mentioned it also doesn't say anything about state space coverage or input argument space coverage or all combinatorial paths through your code. Only that some line/branch has been hit at least once.
As others mentioned it also doesn't say anything about state space coverage or input argument space coverage or all combinatorial paths through your code. Only that some line/branch has been hit at least once.