Correct, as "XT" stands for eXtended Technology. You can't extend it without having the basic technology first. The 5150, aka the PC, was that basic technology. However, in terms of CPU, graphics, sound and all other aspects relevant to this demo, the 5150 and 5160 are interchangeable.

The main differences between 5150 and 5160 are: 5160 upgraded from 5 to 8 ISA slots (also changing the size of the bracket, which has been the standard ever since, even today with PCI-e 5.0). 5160 removed the cassette port. 5160 came with a harddisk as standard (and as a result, a more powerful PSU, as the stock PSU of a 5150 was insufficient for a HDD, and generally required an upgrade).

Memory-wise, there are various different revisions of 5150 and 5160 boards, which can take different amounts of memory onboard. For the 5150, the early revisions took 16k-64k, the later revisions took 64k-256k. For the 5160, the early revisions took 64k-256k, the later revisions took 256k-640k. In all cases it is possible to add additional memory up to 640k via an ISA card. So it is possible to have a 5150 configuration with the full 640k that the most high-spec 5160 had.

Then there is also the IBM 5155, the 'portable' PC. This is essentially a 5160 motherboard in a modified case, with an integrated CRT. As such, it is also fully compatible with the 5150 and 5160, and can run these demos flawlessly.