IMO, there was no 'U-turn' in the side road, the car drove in and reversed out.
The contravention is 50U - performing a prohibited turn (no U turn) in Clayhall Redbridge. There is a no U turn sign which I was aware of. They have provided video evidence but i can’t find the legal definition of a U turn, only it’s a 180 move to point your car in the opposite direction.
Just re-read the OP's post.
They knew of and saw the 'No U-turn' sign. (I thought originally that they were contesting its presence).
Then the OP posted: 'I believed a U-turn had to be a continuous movement causing the 180 degree change of direction'.
However, if they read the High Court judgment they will see how, in the words of the judge, 'absurd' this interpretation is. The judge gave the example of a skilled motorist executing a continuous manoeuvre because they and their vehicle could and contrasted this with a less able motorist and car: the former committing the contravention and the latter not. An 'absurd' interpretation of the intent of the restriction in his words.
OP, the adjudicator is bound by the High Court judgment so I suggest you read this as it will likely answer your question as you've expressed it above.