Swift casts Bool to NSNumber using 'as' operator

I found an interesting code in my project and I'm wondering how it even works. If I simplify it, in a playground it looks like this:

var b: Bool = true
var n: NSNumber = b as NSNumber

I don't understand why as operator casts Bool to NSNumber. Documentation for as gives the only example for using it, namely for checking a type of an element in the array of [Any]. That's an example from Docs and that's how I expected as to be used:

var things = [Any]()
for thing in things {
    switch thing {
    case 0 as Int:
    case 0 as Double:

I didn't expect as to do a real casting. Where can I read more about it? When I try similar code with Int instead of NSNumber, it doesn't compile:

var b: Bool = true
var n: Int = b as Int --> doesn't compile

So NSNumber seems to be a special case? I'm confused. Can anyone shed light on this?