We developed a purely field model of microphenomena - prequantum classical statistical field theory (PCSFT). This model reproduces important probabilistic predictions of QM including correlations for entangled systems. The presence of the sufficiently strong background field is a fundamental element of PCSFT. In the absence of such a field ("fluctuations of vacuum") PCSFT can reproduce correlations only for quantum systems in factorizable states. By taking into account a random background (of the white noise type) we are able to construct the classical field representation in the general case. This has been done under the additional assumption that prequantum random fields are Gaussian. In previous works on PCSFT, Gaussianity of prequantum fields was invented as a purely mathematical assumption - to simplify calculation of correlations. In this paper we present the derivation of Gaussianity by representing the probability distributions of prequantum fields as the limiting distributions of wave-pulse Poissonian processes.