IMO, there's no ambiguity here.
The default position is that footway parking is not allowed.
If the council wish to allow it then, as the OP posted, a sign must be erected to this effect. These are set out clearly in the regs:
https://www.legislation.gov.uk/uksi/2016/362/schedule/7/madediagrams 12-17.
When placed at right-angles to the carriageway diagram 12, as in this case, means that parking on the footway beyond the sign on this side of the carriageway is permitted with 2 wheels on the footway.
OP, you were facing such a sign but you had not passed it. No different to a CPZ sign, or permit parking area, or speed limit for that matter: until you've passed one (or the first onej then it doesn't apply.
As regards parking on the footway, it was not permitted where you were by the sign ahead of you, only beyond the sign.
But being that councils are chaotic, this is not to say that either:
You had already passed one (which had not been terminated) on your route*, or
The council has actually excluded the whole road and been lazy and penny-pinching by not placing signs at the actual point that footway parking is permitted.
*- I can't see one on GSV.