This is irrelevant. The theorems Avigard, Buzzard, et al. are talking about all have natural language proofs already that in theory should be formalizable.
They are not claiming all possible theorems are formalizable. They are claiming to try to formalize all already proven theorems in the mathematics canon.
To the extent the theorems in question are impossible to formalize this means the original proof must be in error.
They are not claiming all possible theorems are formalizable. They are claiming to try to formalize all already proven theorems in the mathematics canon.
To the extent the theorems in question are impossible to formalize this means the original proof must be in error.