What stopped the robber from hitting you with a hammer over your fingers every time you say you don't have any more Bitcoins in some other wallet, he has nothing to lose but a few minutes while if you keep denying you will end without a hand, how long do you think you will be able to hide your second stash and not utter a single word about it in such conditions?
The robber will torture you in this way if they had enough information about you before pulling off the attack, if they know you are very rich in BTC and you are showing them a few hundreds, they are surely going to torture you real bad. I always recommend setting up a passphrase, and loading the base wallet with a convincing amount of money, it can help one claim plausible deniability and if you're lucky it can save you.