Why is there a plus sign inside of the macro implementing Add for numbers in Rust?

Hello!

While looking into Rust's implementation of the Add trait, I noticed that the add method has the expression self + other. I find that intriguing because isn't + the same operator that this implementation is defining behavior for? What implementation of + is add calling here, if say u8 doesn't have that behavior defined yet? Like in fn add(self, other: u8) -> u8 { self + other } for example.

Here is the source code of the macro:

macro_rules! add_impl {
    ($($t:ty)*) => ($(
        #[stable(feature = "rust1", since = "1.0.0")]
        impl Add for $t {
            type Output = $t;

            #[inline]
            #[track_caller]
            #[rustc_inherit_overflow_checks]
            fn add(self, other: $t) -> $t { self + other }
        }

        forward_ref_binop! { impl Add, add for $t, $t }
    )*)
}