Question regarding to public and external functions in auditing Lydia Finance

Hey guys, I just read a Certik auditing report for Lydia Finance and noticed the section on PG 12 is highlighting using external instead of public visibility for gas optimization, but I did some simple tests given below and found no difference between public and external visibility in gas consumption. Wondering if I am missing anything. Thanks.

// SPDX-License-Identifier: MIT

pragma solidity 0.8.4;

contract Test {

    uint256 private val;

    function setVal(uint256 val_) external {
        val = val_;

    function getVal() external view returns (uint256) {
        return val;