Trist and Ezreal have kind of unique "dash" abilities. Tristana's is a kind of prolonged kha'zix E, however the mechanics of it is as follows: She has a very short, <0.25 sec, windup time before she actually leaves the ground. When she has left the ground however she removes any cc that changes her position, for instance the Blitz grab. What you see is the hook landing on her during her windup time, when she is on the ground, and you can actually see her being pulled ever so slightly for a fraction of a second before she finishes the windup and enters the second phase of the rocket jump, which changes her direction. So an easier, and more correct, way of explaining it is this: Let's say trist is moving to the left, Blitz grab will change that to right by force, however if Trist can time it correctly she can let the Blitz land the grab whilst she is channeling the rocket jump, and then rocket jump makes her move left again. <<<(normal movement) >>>(Blitz grab) <<<(rocket jump movement, if blitz grab hits BEFORE it executes upon the successful channeling of the windup time).
The Ezreal mechanic is a bit more difficult I think, but works on the same logic. With Ezreal's E he also has a windup time, he channels for a fraction of a second before it executes, making Ezreal stand still for a short duration before it goes off. A way to see this clearly is by comparing to Zed's Shadow Dash (W). Zed can place a shadow and upon clicking the button again he instantly teleports, or blinks, to the shadow with no duration. However Ezreal DOES have a duration. It works like the tristana rocket jump. Here is a breakdown of a successful cancellation of a Blitz grab with ezreal's E. First blitz must use his q, then ezreal has to time it so it lands on him whilst he has just finished channeling the E. This is one move command, Ezreal's normal movement, interrupted by another move command, blitz's grab. The third move command coming from ezreal is received upon the completion of the E channel, which cancels Blitz's move command on Ezreal, and places Ezreal somewhere else.
The reason these characters are the only ones who can do it - I think so atleast, you'll see why - Is because no other champions with "dash" abilites have a windup or channeling time before the actual movement displacement command executes. That's why for instance a Lucian E isn't able to cancel a Blitz's grab, because his E is instant and he only has one move command which isn't prolonged. You CAN still grab a Trist or Ezreal, you just have to be smart about it. When trying to grab a trist don't aim for where she's standing, aim a bit in front of her to interrupt the second move command she issues, she has no way of canceling the grab whilst in the air. For Ezreal, well you're gonna have to madlife it a bit and try to predict where he'll E to.
This asymmetry isn't really impacting on the player base as a whole because the overwhelming majority of players are at a skill level where this mechanic is near impossible to execute properly, or they simply don't know it exists. In high Elo however, in high diamond, masters, and challenger, and even in pro play, this can lead to some really cool outplays. The supports know that this mechanic exists, and so do the ADCs. This leads to this not being a matter of "can you do it?", it turns it into a mindgame of "when is HE going to do it, can I time it correctly?".
The thing also is that, if you want to climb in ladder then this type of stuff is maybe 10% of the way to climb. 90% is game knowledge, it's knowing what to do in a certain state of the game and how to do it. That is what seperates the challengers from platinums, at about diamond 2-1 the mechanics start to level out where in high Masters it's pretty much at its peak - save from exceptions like Faker who somehow break even that upper level of play - and after that it's ALL about knowing the strategies and tactics of the game. Wave control, objective control, vision control, rotations, and all that.
tl;dr
Ez and Trist have 2 phases of movement in their "dash" abilites, one where they channel for a fraction of a second, and a second where they exectue the movement displacement. Grabbing either in their first phase results in the grab being canceled by their second phase. To outplay this, aim further up vs Trist - to grab her in the air where she can't input any more delayed movement commands -, and predict like madlife vs Ez. No other champs with dash can do this because all other dashes are instant or don't have multiple inputs of movement commands.
