Acacia baileyana will hybridise with a variety of similar bipinnate wattles. A clue would be to see what is in the vicinity of the suspect plants. The progeny of hybridisation of two species create what is known as a hybrid swarm, with plants resembling their parents in a very highly variable set of characters. Some plants will differ very little, if at all, from one parent or the other, while others can range anywhere along a continuum, sharing and/or blending the set of characters of both parents. This does not just mean leaf-shape and colour, for example, but also inflorescence architecture, bark type, and habit of the mature plants. Having said that, it is most likely that this specimen is indeed a hybrid between A. baileyana and A. decurrens, given the foliage shape and colour, and importantly, the fact that both species flower at the same time, which is essential for cross-pollination.
My apologies, on looking at the photo again, I’d be prepared to say A. baileyana x A . dealbata. I had the image of the other hybrid in my mind when responding to this one.
Rainer, from the hairiness and colour it looks as though it has dealbata parentage but the number of pinnae is low. As you say, resemblance is highly variable so this might just be a baileyana characteristic coming out.