The linesman flagged it offside, Walsh was off his line so it's hard to tell, I'm going to trust the lino.
I'm refrain from using terms such as white stick, but will instead refer to white line that marks out the six yard box. Goal scorer outside it and defender inside it, maybe the lino thought the defender was the goalkeeper, it was the only conclusion I could come to.
Your right about the defender in the box, but there needs to be 2 players to be onside, as our keeper was awol Who else was playing him on?
Before the ball was played by the opposition and excluding our guy that ran into the centre of goal, while the keep is awol, there was another player of ours that ran round the back of the keeper and although we can't see it from the linos position but it looked like that played him onside. Look at 3.50 to 3.51 of the video and look directly behind the assist on the ball - our player may be obscured slightly due to the angle of the camera.
To me Bromley's goal looks perfectly valid. Appreciate the camera view isn't anywhere near but the "goalscorer" was definitely onside have been played on by one of our young pros playing at centre back.