A quick question about how to move turbo boosting units correctly =)

During a game between two friends last night one of them pulled a move that I feel I could use with my Reavers, but I'm not absolutely sure if the move is legit.
He deep striked a unit of Screamers 10" away from his opponents' zombie blob. In the shooting pahse he declared a turbo boost, so far so good, but it's the way he moved the screamers that annoys me a bit.
The Screamers wouldn't be able to fly over the whole zombie blob so instead he moved 6" in a straight line as far as possible over the zombies and then he moved back again the exactly same way and claiming that he just turbo boosted over the unit and that the zombies got hit by his attacks (screamers has similar rules like our blade vanes).
The moving pattern was not a circle or U-shaped, but a straight frikkin line (??) is this really a legit move patter?

as for turbo boosting, yes, he could do that (you can move any direction, so he could of moved 6" forward, and then 6" back, still claiming the coversave)

As for the slash attack rule, I know its not written exactly the same as reavers bladevanes, but as for reavers bladevanes, you have to draw a straight line from their starting point, and their ending point. So even if you move in say... an L pattern, if the squad isnt under that straight line, then they dont get hit. Im pretty sure slash rule works the same way for the screamers, the only difference I know is they tell you where to take casualties from, instead of the random.

so no, he could not do that. As the squad is not under the line drawn from the starting point to the ending point. (that is if the slash attack rule is an exact wording from the bladevane attack)

I had a similar experience with a friend of mine who plays necrons using his chariot to make L shaped or U shaped moves with the chariot special attack, and we made the same determination- the rules seem to suggest that you measure from point A to point B rather than assuming a move in some other formation.

Cheers,
Nick