What I can guess is that the car you saw isn't actually a 1.6 GLI Auto but a regular GLI 1.3 in which someone has put in 1.5 Axio Engine and a 1.6 badge to make it look like 1.6 GLI Auto.
This swap from 1.3 to 1.5 makes sense, because whoever did it wanted an economical and powerful 1.5 auto car by investing around Rs. 100000 on a regular GLI.
If it was already 1.6 then this swap would not be justifiable because the starting price of 1.6 GLI is already too high to do such a modification only for the heck of it. But if it was done because it's engine got damaged, the more feasible option would have been to replace the 1.6 with the same engine so the car doesn't lose its value.
So explanations aside, the swap is really easy. The engine fits bolt on, and if you have the complete wiring harness with the engine, there's no modification required at all.
It should work like a charm.