5 year old boy freakishly terrified of zombies!!

This boy's grandmother in Thailand would always put a red blanket over herself and knock on the window while mommy says "the zombie is here because your not listening! You better listen and the zombie will go away". Personally I knew it was causing mind problems for him and I told them to stop, but in their opinion it was to get the kids to "listen"....when my kids came to Canada I tried to fix what he was brainwashed with and told him many times "there are no zombies in Canada", but that doesn't seem to change anything. Thailand has the weirdest tactics on raising kids (which I never approved of because it was only planting fear in their heads and this is cause and effect of how they used "zombies" to teach the kids.)