He doesn't mean only when player is completely trapped, What he is referring to is an old known bug on few XML engines 8.00/8.10 where in specific positions/situations one player can attack but the other won't be able to attack back.
I will post this gif showing which position are used to be able to attack without being reached by the other player, When
Test Three
stands on any of the
100 crystal coins
positions he'll be able to attack
Test One
, But in the opposite
Test One
won't be able to attack him back on those specific positions, So it looks like this.
View attachment 60882
So players who are still playing XML servers 8.00/8.10 are far used to this PVP style/tactics that most of them don't even recognize it is a bug and they think that's how the game works.
They use it in many different situations like in this example.
View attachment 60883