ContainsRune给出奇怪的结果

I'm running this code in Go Playground:

fmt.Println(strings.ContainsRune("\xa0", '\xa0'))

I'm wondering, why does it output false? According to the docs, it says:

ContainsRune returns true if the Unicode code point r is within s.

It seems to me that the code point is there, it seems strange that it would give false as a response.

"\x0a" is not a unicode code point.

fmt.Println(strings.ContainsRune("\u00a0", '\u00a0'))

Works, as expected.

Because it's not a valid unicode code point, looking at strings.IndexRune

func IndexRune(s string, r rune) int {
    switch {
    case r < 0x80:
        .....
    default:
        .....
    }
    return -1
}

If you try utf8.ValidString("\xa0") it will return false.