1. If an outside-the-system observer cannot detect any flaws in what a RNG outputs, does the outsider have any basis for claiming a lack of randomness? Practically speaking, randomness is a matter of prediction based on what you know.
2. AI just means “non human” intelligence. An AI system (of course) can incorporate various sources of entropy, including sensors. This is already commonly done.
Heuristic or not, AI is still ultimately an algorithm (as another comment pointed out, heuristics are a subset of algorithms). AI cannot, to expand on your PRNG example, generate true random numbers; an example that, in my view, betrays the fundamental inability of an AI to "transcend" its underlying structure of pure algorithm.