I google this and found just a tiny sentence,, but the link lead to info that didnt mention apples at all. Perhaps, maybe, guessing, that the calcium helped your apples be healthy and fend off that brown rot. Now you have me searching for more confirmation; certainly brown rot is not among the top 4 disease issues...... but when it hits, it feels like it!
https://www.starkbros.com/growing-gu...bout-brown-rot