Could have been a case of a very heavy A340 rotating a long way down the runway and RYR not so heavy and knowing he was going to be airborne way before where the A340 rotated,and would be above the 340's flight path during the climb out - its called exercising one's discretion!!!
Unless, of course, one has a donk stop apres V1
Yes, I know, I must be getting to be a boring old woman.
Not wishing to teach egg sucking but remember that a slight x-wind could hold the vortex on the runway.
I posted on another thread about tiles being removed from roofs that we'd been having a beer close to an airport one evening when a vortex arrived on the terrace - quite invigorating.