Like nearly everything that occurs in the atmosphere, what causes a block is complex and there isnt a singe cause.
Google this- "what causes an atmospheric block"
I think it will help you get a better understanding.
Maybe google atmospheric block- there are several types. A NAO block is a Rex- poleward ridge/ equatorward trough. It forces the flow to buckle southward and that places the baroclinic boundary further south- meaning storms develop/ take a more southward track.
I answered it above. A block means a ridge/trough combo(eg rex block) that remains stationary/quasi stationary. A transient dipole does nothing to help our cause unless literally everything is timed perfectly.
To me its just wonky and not a useful block. Not really a block at all. That's a snapshot but everything is in motion. That trough over the Canadian Maritimes becomes a ridge a day later. That's probably what's meant by 'open Atlantic'. Shit be moving- no block in the flow.
It is stronger and sharper with the NS vorticity but digs it southward a bit too late. Still a minor improvement at the surface and a trend towards the Euro.