It’s not going to reveal anything, there were probably hundreds of tourist visas refused at that consulate just this month alone. It’s just whether or not it’s a high risk consulate so advice can be more tailored.
But if you don’t want to say that’s fine. Your BIL can try again, although not straight away as that would be a pretty much guaranteed way to throw that money away, he should leave it a while and then try again. You can’t ‘sponsor’ him but he can say you’ll support him financially if he gets the opportunity, but stronger ties would increase his chances far more i.e. waiting until he’s finished studying and got a full-time job/his own home/a spouse.
And just checking, but you haven’t filed a I-130 for him at any point?