Detecting a UTF-8 string with control characters leads to unexpected behavior

[ruicc]

import Encoding from 'encoding-japanese';

const bs = Buffer.from(new Uint8Array([0x08]));
console.log('detect("<BS>"):', Encoding.detect(bs));

const utf8str = Buffer.from("UTF8の文字列です", 'utf8');
console.log('detect("UTF8の文字列です"):', Encoding.detect(utf8str));

const utf8BS = Buffer.concat([utf8str, bs]);
console.log('detect("UTF8の文字列です<BS>"):', Encoding.detect(utf8BS));

output:

detect("<BS>"): ASCII
detect("UTF8の文字列です"): UTF8
detect("UTF8の文字列です<BS>"): UNICODE

I think the final result can be "UTF8" because UTF-8 includes ASCII.