How could an inflation bug be spotted in grin? Looking at the transactions within the block explorer I can't see any transaction amounts. How could an inflation bug be detected if all transactions are private?
Range proofs for CTs demonstrate that output amounts are positive and within an allowable range, and that no inflation is occuring in a non-coinbase transaction.

The range proofs (eg bulletproofs) are computationally binding. 

If the discrete log is broken, range proofs can be generated for values outside the correct range without any way to detect this. This includes correctly validating proofs for a tx with inflation.