These nodules in a leaf may be some sort of gall or insect larvae. I cut one open and could only see light-coloured fleshy pulp (no obvious insect or egg inside). I have never seen these before and have no idea what they are.
Looks rather similar to the galls of midge Austroacacidiplosis botrycephalae but on a different type of wattle - see Austroacacidiplosis botrycephalae Do you know which wattle it is?
Yes, it is definitely a gum leaf. I think a cockatoo snipped a small branch which fell in front of me as I was walking through the forest. I have taken a photo of the tree that I think the leaf fell from at the following URL https://photos.app.goo.gl/fkqWVeYszHyypfJWA