Why does Laravel Sanctum append token key to the plainTextToken?

Referring to the following code from Sanctum:

public function createToken(string $name, array $abilities = ['*'])
    {
        $token = $this->tokens()->create([
            'name' => $name,
            'token' => hash('sha256', $plainTextToken = Str::random(40)),
            'abilities' => $abilities,
        ]);

        return new NewAccessToken($token, $token->getKey().'|'.$plainTextToken);
    }

Source: https://github.com/laravel/sanctum/blob/31fbe6f85aee080c4dc2f9b03dc6dd5d0ee72473/src/HasApiTokens.php#L44-L53

Why does Sanctum append $token->getKey() to the $plainTextToken? In other words, what is the purpose of the $token->getKey() part? Is it used during authentication as a key to retrieve the encrypted token string and compare it using Hash::check or something?

I have another question: The migration that creates the personal_access_tokens table indicates that the token column is unique. However, in the above code I can see that the value stored in the token column is just a hashed value of a random string hash('sha256', $plainTextToken = Str::random(40)). Does the hash function always return unique values so that it doesn't violate the unique constraint?

My first thought was that the $token->getKey() should be appended to the encrypted string to make it unique. But I think this is not the case.