Ed's streetview is from a ped Xing, and there's no indication that you can ride a bike on the pavement there.
A little further round there is a dropped kerb (the entrance to Clarence Street) with a pair of full-size no-entry signs on it.
A little further round again there is another dropped kerb (the entrance to Castle Street, where you can ride) with a full-size no-entry sign, with an "Except Cycles" underneath it.
That little sign looks like it's just a reminder. Apart from this, I think it's pretty clear (in this direction at least) that you're not meant to enter Clarence Street from this end on a bike.
At the other end of Clarence Street, I think you have those empty red circular signs that mean (and say) No Vehicles, which includes bikes. (No Motor Vehicles has a car and a motorbike in the circle). So, as long as you know what the signs mean, it's quite clear that you shouldn't be riding there, I think.
I wouldn't challenge your FPN. Sorry.