Zain's an acquaintance of mine and I've personally seen this car go through the transformation, I was there at the workshop during the days it was getting swapped, since work was being done on my car as well.
I'm not taking anyone's side here but yeah the 7 second figure on an automatic transmission Corolla seems unrealistic, no offence.
So does the 3.8 second with the new engine, yes I've seen the car's runs and I'm pretty sure the actual 0-100 time can't be calculated by the speedometer due to wheelspin, the 3.8 figure is clearly based on wheelspin.
The only way of finding out the actual 0-100 would be using a GPS based device, simple.
I don't have anything against anyone, I'm just stating this from experience.
My car was doing 0-120 in 5 seconds according to the speedometer but that was all because of wheelspin, it was actually doing around 8 seconds when measured from an authentic GPS, this was on my set of 205/50R15 Traction AA rated tires.
Peace.