Computers are purely deterministic indeed.
This is not true either. Computers produce inexplicable glitches, some of which can be attributed to quantum effects at the ragged edge of expected distributions. In fact, the design of modern computers must cater substantially to quantum random effects thru redudancy, and error detection and correction.
In fact random numbers are quite hard to achieve in computers.
This is not relevant. This is a specific incomputability problem. At any rate, it isn't difficult for stochastically sophisticated programmers and EE's to produce random numbers on a computer, it is only hard for unsophisticated programmers who don't know much about anything but code to generate random numbers.