Help! How do I prune young Robinia?

In the last picture it looks like it was pruned and the branches died back, probably due to them not pruning back the leader at the same time.

Doesn't look like the graft is up that high anyway, unless its at the point just above the two dead side shoots, in which case, why didn't they cut those shoots back flush to the stem.

I dont think you have a dwarf tree, it has the potential to be fairly large, maybe not like an oak tree but a fair size.
It looks to be fairly vigorous in growth, to me.

 

@GardenJoy this is what a top graft looks like on my very short crab apple


You can see a very clear difference between the two parts.
Tbh @Thevictorian , what looked like a rootstock graft last year now seems to have just been lumpy growth!

 

I think if you look at the above image, unless it's my eyes, you can see the graft on the left thicker trunk at the v. This is how top grafting is normally done with these. The shortened branch which has sent up two new shoots, is left as a sap draw, until the graft has healed and then cut off. I wouldn't do anything without checking that it is definitely grafted but you only want material from above this graft left. Anything below that point though, I would remove without leaving stumps.

 

@CarolineL those knobbly lumps on the root stock are where they want to send out new roots. If you buried it deeper they would continue to grow but as they are above ground, they just get air pruned.