Well it's not odd. A hungry spider will try to kill anything to scale that moves and wanders within its sight. It's just that mealworm beetles are not really a good food source since most of their mass is just a hard chitin shell. They don't really benefit from a such diet. It won't harm the spider, but the nutrient % is near to 0
I love it when one of my spiders takes down a beetle. (I don't include the beetles as a staple diet, just every once in a while).
My B.kahlenbergi loves them. Or hates them with a passion since it takes the beetle down mid air usually. And then it goes CRUNCH and I had fun as well