"Iconic" can be a bit vague in this case. But if he means "most unattainable", then it's an incorrect statement. The iconic record that will never be broken is Dimaggio's 56-game hitting streak. A couple of guys got into the 40s before the semi-intentional walks began to make a mess of their streaks.
And even if that scurrilous scheme didn't occur, hitting 56 games in a row is dicey at best. You've got to have incredible bat control to even approach 56. Most guys today don't even recognize the concept of bat control.
I think Nicklaus's 18 majors will never be broken, especially given the way the PGA is screwing up everything lately. All the good players will go LIV soon.