Apparently it has been tweaked. I've read in some news and on wikipedia that the engine used is the Valve's Source Engine. http://en.wikipedia.org/wiki/Titanfall http://games.on.net/2013/06/respawns-game-revealed-as-titanfall-a-source-engine-multiplayer-game-with-giant-mechs/
There's a download link to the gameplay demo at 60fps in the official site, 1,2GB but i deserves the time :) Is that true that all this is on source engine? it may be not very next next gen, but the gameplay is amazing.