Beginner and understand owner renounced and backdoors

Smart Contracts
1

Hi,

I'm a beginner learning solidity but also I like to invest in tokens and my concern is possible back doors. This contract is renounced but is it safe? There's a function with bool, does this void the renounced owner?

pragma solidity 0.6.12;

import "@openzeppelin/contracts/GSN/Context.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract Operator is Context, Ownable {
    address private _operator;

    event OperatorTransferred(address indexed previousOperator, address indexed newOperator);

    constructor() internal {
        _operator = _msgSender();
        emit OperatorTransferred(address(0), _operator);
    }

    function operator() public view returns (address) {
        return _operator;
    }

    modifier onlyOperator() {
        require(_operator == msg.sender, "operator: caller is not the operator");
        _;
    }

    function isOperator() public view returns (bool) {
        return _msgSender() == _operator;
    }

    function transferOperator(address newOperator_) public onlyOwner {
        _transferOperator(newOperator_);
    }

    function _transferOperator(address newOperator_) internal {
        require(newOperator_ != address(0), "operator: zero address given for new operator");
        emit OperatorTransferred(address(0), newOperator_);
        _operator = newOperator_;
    }
}
2

If you call the function renounceOwnership(), that means the new owner will be the address(0), and this account does not be in controlled anyone, I think this is safe.
And what is your meaning backdoors?