TP inside arena game?

So.

Me and a guildie tried to do some fun 2's.
We met this arms war and hpala.
Arms war went lolstorm and retaliation and i followed him down. (don't say anything, i was bored)
All of a sudden he's up next to his paladin buddy. You physically can't intervene there.

It was close to the boxes / right under then boxes in Dalaran Sewers.

TP hack? I'ma record a few games and study it but both of us went pretty stunned when we saw him porting up there.

You should be able to replay the match by its id (which can be found on the armory history if it was ranked game) and eventually report it ingame to the staff