It seems this superstition is a thing - Superstitions about the Monkey Puzzle tree can be found throughout Britain. One widely-shared bit of folklore is that the Devil himself sits in this tree and people have to be quiet when walking past or else they will attract the Devil’s attention and get bad luck. In some cases this was to be bad luck for three years.
https://www.heywoodhistory.com/2012/09/the-devil-and-monkey-puzzle-tree.html
I have no time for superstitions and never will, touch wood, but I don't see what you can do to change your husband's mind if he is determined.
What would he do if your next-door neighbour planted one in his garden tomorrow?