I'm going to go out on a limb here and make a wild guess.
That boolean is actually mostly an extension of the integer system whereby we now have an integer type that stores only one bit.
Whereby the bit stored either results in a 'true' or 'false' value.
Anyways, I know booleans are useful in systems development when you have strict memory / storage constrains / bandwidth (networks).
Yeah, that works for me.
'bool' is still at least 1 byte in C. If you want to store one Boolean per bit you have to manually implement a bitmap.
The way C handles (prior to C23) booleans is pretty close to how you'd handle booleans in assembly.
CPUs don't have types, everything is integers or floats. You do your work on registers which have fixed sizes. CPUs have built in instructions for "is this register not zero" which leaks into C. 1 is true in C, but so is 2.
Also, single bits are rarely used for booleans because it requires more CPU power to extract a single bit. Everything is byte aligned at a minimum.
When doing something like network code, if you want to store a bunch of booleans you are typically going to either pack them into a byte, or you'll burn the extra bits and send a single byte for the boolean value. Typically this was flags and masks.