-.- Yeah because it couldn't have been done by something with.. oh I don't know... a BOMB! You guys are seriously targeting that this was Nova WAY too fast. So before we move on, let me give a rough detail just so that I can feel a bit better about continuing.
The explosion has toppled the building that Austin was standing on as well as the two buildings to Nova's right -- though only the front sections as the back of both buildings maintained its structure. This means only three buildings were affected physically in the wake of the strike. The center of the destruction would leave nothing but a dome in the form of a crater, this represents the outward explosive force sent from Nova. While there are traces of fire around the area, the fire is no different then that which follows destruction meaning it could have been caused from an explosion; and in fact, was. The important thing to note isn't the FIRE damage, but the multiple lacerations over walls and pavement from the highly sharpened wind which means that a fire user couldn't have caused the damage, it was caused by an explosion being contained by wind currents. Along with that, there are people nearby, witnesses, who are now watching the Titan's as they gather, as they were walking nearby when the battle began -- though none were caught in the explosion. These witnesses can be used to decipher what happened. Notably, a small pile of debris would have been pushed out of place, leaving a clear spot hinting that someone was there and moved from that location. Upon closer inspection ONLY by those with very keen eyes might note the print of a fist dead center inside of the crater. This would be disturbed due to the debris falling into the crater.
Ending Conclusion/Theory. It was impossible for anyone to have told that Nova did anything (or even that a fire user did anything) just by looking at the scene. The only descriptive sights would be the tears from the wind since Nova's fire never went anywhere past the walls of wind and the crater which could have been made by an explosive.
I'm sorry if I'm getting harsh or anything, but both Red X and Athena have narrowed down instantly that it must have been a fire brand and it's 100% because you guys read that it happened. It's upsetting for me. I'm sorry that I reacted like this, I just had to say something before someone else showed up and did the same thing.