The idea behind pseudo-random number generators is to generate random numbers using the software, which is convenient and cost-effective. The pseudo-random number generators are one-way functions so if you know the seed you can predict their subsequent values but you cannot determine the sequence of values if you do not know the seed. Quantum randomness is physical randomness or the so-called true randomness. Mathematically, they both have the same statistical properties; provided large number of values are sampled from both of them. Thus, a well designed pseudo-random number generator would be as random as Physical (True) Quantum random number generators, so if you do not know the seed, you will not be able to distinguish them. The advantage of Physical (True) Quantum random number generators is that you cannot guess their values in any case.
If the pseudo-random number generator is not well designed then you can identify patterns in it like the infamous RANDU routine (https://en.wikipedia.org/wiki/Randomness_tests), which fails randomness tests.
In practice, physical source of randomness is often XORed with pseudo-random numbers to pass the randomness test. You may refer to https://en.wikipedia.org/wiki/Random_number_generation