Almost all idioms we use commonly actually originally meant the opposite. "Blood is thicker than water" is a longer saying about chosen family being the true strongest bond. "Great minds think alike" finishes with but fools seldom differ. A few bad apples, spoil the bunch. "Pull yourself up by your bootstraps" only a fool would try it. It's the most human thing in the world to twist sayings to mean the opposite.

all intensive porpoises

100% thought it was a diamond among common stones. I think that misunderstanding began with the movie Aladdin.

Deal with this all the time. I never trust an archaic term because of how many common archaic terms are like that, or worse, with their implications. And idioms like you are citing are really common. A favorite of mine is counting how many famous idioms are just considered excuses to go to the restroom in the Midwest. See a man about a dog? Poo. Take a constitutional? Poo.

Words do evolve and change meaning over time. The Flintstones had a 'gay old time' for years. Verizons 'unlimited internet' package is not without imposed limits, and the 'Burger King' is permitted to make the shittiest burger ever.