correction: they train you to disarm an unwary opponent who is foolish enough to approach within three yards.
"point blank" for a pistol is (generally) the distance between fifteen and thirty yards. This term has to do with the dual intersection of the ballistic arc and the line of sight in a typical azimuth, wherein the elevation deviation in the distance betwen those two intersections is insufficient to cause deleterious effects on point of impact vis a vis point of aim.
despite the term "point blank" having a specific meaning, it is often mistakenly used as a synonym for "contact distance" or "arm's reach"
More importantly, "disarming moves" only work if your opponent is unwary, caught off guard, and has poor reflexife reactions. Use of a disarming move is a high-risk option, even for an expert.
Odds are good you will eat a bullet if you try it.
It's actually extremely easy to take a pistol away from someone who's stupid enough to be satisfied with pointing it at you at arms reach. It's the guy who's smart to be shooting at you instead of holding you at gunpoint that's going to ruin your plans of disarming him. It's actually incredibly stupid to staticly hold any weapon with an outstretched arm within arms reach of an opponent.