That looks like the bows have ridden up on something under the port side as it exited the lock, possibly the motorbike shown in the other photo. This would have lifted the port bows up and tilted the boat over to starboard, jamming it in the lock exit with the top starboard rubbing strake wedged against the wall. If the boat was going ahead when this happened it could have been firmly wedged, and it would be difficult or impossible to free it by levering with the plank as shown.
Probably the only way out would be to pull the boat backwards by going astern and hope that this pulled it off the obstruction, but if this had rolled forwards when the boat got on top and lifted the hull up even that might not work. Depending how the rubbing strake is wedged into the bricks, even raising the water level could very well make no difference (or make it worse), the bows will just stick there even if the stern lifts -- and if it doesn't and water floods into the boat, you've got a sunk boat.
I suspect the only way out would be to pull the boat backwards with a winch, but they didn't have one and there's probably nothing to attach it to down near boat level anyway -- pulling upwards with a winch attached at lockside would lift the stern and make things even worse.
Alternatively put a *big* bow fender on and use another boat in the pound below as a drift <THUMP> to try and knock the boat backwards into the lock -- after getting the water level back up to where it was when the boat got stuck... 😉
...which would have wedged it in even more firmly if the port bow was sitting on top of something... 😞