IMO, the reason why u can cycle the tank so fast is because of the following reasons;
1. it is an existing tank.. and u merely cleaning it and not nuke them like pouring bleach for a thorough cleaning .. both the media still contain some form of bacteria from the previous tank.
2. u seed the tank using the previous tank's stuff such as old tank water.. basically, it is more like relocating them and changing water lor... thus, u will not get the spike in ammonia as expected.. but this is not to be done for new tank with everything being virgin in that sense..