Reuse Patterns - Regular Expressions

I’ve just completed the challenge on Reusing Patterns Using Capture Groups, and I’m wondering what the extra 42 is at the end?

let repeatNum = "42 42 42";
let reRegex = /^(\d+)\s\1\s\1$/; // Change this line
let result = repeatNum.match(reRegex);
console.log(result);

Returns: 42 42 42,42
Even the example shows an extra string.