I never knew that they incorporated mini games while loading on the spectrum. It will have probably been Mastertronic again as a rough uneducated guess.
Loading mini games was done towards the end of the lifespan of the 8bit era though. What really killed the C64 was the C64 C in my eyes, with just the cartridges and no interface to attach a disc drive or tape loader. Unfortunately it had no access to the huge catalogue of older 64 games so it wasn't really going to go anywhere.
At the same time the Amiga had just dropped in price also, so a lot of people just went for that. Even I started using the C64 less and less once I got the Amiga.