No definitely not a Dendrobium speciosum. The Sydney rock orchid doesn't have those leaves coming out mid stem and/or a sectioned bulb stem like that. It just has the one bulb like stem with leaves from the top.
It does look like it is is one of the Dendrobium family but there are so many species in that family with these segmented fleshy stems that it is difficult to tell them apart until they flower. Suspect it may be Dendrobium nobile, as this is pretty common, but it could well be Dendrobium officinale, Dendrobium anosmum, dendrobium parishii,Dendrobium moniliforme or a number of others - all have that segmented stem.....
Size of the plant and flower shape and colour will help you identify when you get that it may become clearer
Enjoy it - I find some of these lesser known varieties are fantastic, hardy and pretty much look after themselves!