Yeah English is not a clear, direct language.

When English speakers say someone gets defensive, it usually doesn't refer to literally the act of mounting a defense, without any moral connotation.

Instead, they usually refer to someone telling on themselves, by mounting a defense where there was no attack intended on them.

Like that recent trump interview, where pedophiles got mentioned, and he immediately "got defensive", screaming that he's not a pedophile, even though nobody made that statement about him in that interview.