It could be using Huawei software and hardware. Serbian ISP "Telekom Srbija" which uses mostly Huawei HG8245Q2 ONTs and has standardized on Huawei OLT and Core network, also uses these Nokia branded devices. AFAIK the Huawei GPON network is incompatible with other vendors which is why there's a small part of the capital city Belgrade stuck on old ZTE CPEs as that was a part of a pilot FTTH project with ZTE before China financed this rollout.

So, my point being, given they also use this exact Nokia ONT, it could very well mean that it's compatible with Huawei because it IS, in part, Huawei.