I didn't quite understand why they couldn't put one and one together.
"They" could. Did you expect them to liquidate their profitable business model? Peddling superstitious nonsense is a known money maker.
Maybe the RCC, but I respected the Brothers (most of them) that taught at the school. Like I said, it was education first. No indoctrination, even in the religious courses. Taking a course that involved Buddhism was required for all students!
When you are young and don't know a lot of things it can seem like that.
When I was young, just by reading the Tanakh I was generally able to place the time of authorship based on a couple of historical details. I understood context back then, quite well.
Education was their mission. This wasn't some BS far-right wing school. My understanding is that smart, the really smart folks, can just need to believe. Regardless what the pieces of the puzzle say.
Regardless, I'm pretty certain the Brothers who taught at that school wouldn't remotely support this BS. I don't recall seeing any Ten Commandments in the school, anywhere. Crosses were bountiful (as would be expected), but that was it.