You can lock people inside barriers, but I'm pretty sure Zephyr is referring to the trick where a Dainn will carry someone to a corner and then use Ice Wall to create a triangular prison that you can't escape. At that point, the Dainn is free to nuke a more or less immobile target.
The other one is probably something like this, where x
is the Dainn and he uses an Ice Barrier to make it so you can only approach from two directions.
Personally I'm inclined to say the 2nd is just using your skills intelligently. The first one is too, really, but it feels like it could screw some people over really badly. Could a Tia do anything if a Dainn decides to stand right outside the wall out of line for a shuriken and Meteor/Red Fire Dragon?